利用微波加熱進行下水污泥與銀合歡共焙燒之研究

Abstract

自十八世紀工業革命以來，人類活動大量開發化石燃料。然而，在化石燃料蘊藏有限之條件下，亦積極找尋其他替代方案作為能源使用。生質能被視為最具潛力之可再生能源，在避免與種植食用作物爭地的前提下，可經由常見廢棄物如農業廢棄物、畜牧廢棄物進行轉換生產。 本研究藉微波誘發焙燒進行反應，將污泥添加銀合歡製成混合材料，經熱化學轉換，提升產物特性，進而產製生質炭，作為替代燃料使用。以微波進行加熱反應，相較於傳統加熱，不僅能減少能源消耗，對於產物反應效率亦能大幅提升；焙燒反應為低溫碳化反應，可保有較高含量生質炭。固態產物分析項目包含熱重分析、重量產率、能量分析、熱值分析、近似分析等，分析產物性質變化，最後以生命週期評估，評估投入與產出之衝擊與效益。 實驗操作條件設定為30分鐘，微波功率應用於污泥及混合材料分別為100-400 W及100-350 W，污泥混合比例為25 %、50 %、75 %。結果顯示，經熱重分析儀測定污泥材料大量散失主要位於溫度200 °C至500 °C之間；重量產率中，污泥單獨焙燒整體隨功率升高，而呈現重量產率下降，微波功率升至250 W以後，污泥僅剩不到投入之一半，功率400 W重量產率為最低值20.48 wt. %。污泥添加銀合歡進行共焙燒反應中，於低功率100 W條件下，污泥混合比例從0 %提高至25 %及50 %時，可觀察重量產率呈現明顯直墜情形，表示污泥添加銀合歡共焙燒能提升整體裂解情形；熱值分析中，污泥除了功率100 W所產生之熱值些微高於原始污泥之外，其餘功率下熱值皆低於原材料污泥。污泥混合比例25 %中，於低功率100 W，熱值可與銀合歡產物相近，可表示低混合比與低功率下能保有產物之熱值表現。 污泥經焙燒後產物之近似分析中，功率250 W至400 W時，揮發分比例僅剩含量介於1.9-4.8 %，灰分比例提高至64.61-72.34 %，固定碳介於30.63- 25.74 %；元素分析中，污泥以Van Krevelan Diagram進行比較，當低揮發分煙煤與產物於功率300 W之H/C值較接近。污泥共焙燒於比例25 %與50 %中，分別以功率350 W及功率150 W較接近低揮發分煙煤之特性。生命週期評估部分，污泥焙燒主要成本投入在於污泥含水量(85 %)於烘箱乾燥單元，可高達292 kWh，表示污泥含水量對於污泥處理為一重要指標。污泥與銀合歡共焙燒可降低污泥乾燥投入成本，亦可保有產物含量較高之熱值。

Due to the demand for fossil fuels which have been mined intensityly since the industrial revolution in the eighteenth century. However, under the conditions of limited resources, alternative energy must be found. Biomass can be considered as a potential energy development via common wastes conversion, such as agricultural waste, and animal waste. This study was carried out by microwave-induced torrefaction, which is a thermo-chemical convertion techmology to react mixed materials, including sludge and leucaena which acts an additive to improve product properties. The microwave heating reaction compared to conventional heating, not only reduces energy consumption but enhances the efficiency of the reaction. Torrefaction reaction is mild pyrolysis treatment which retains higher contents of biochar. Solid analysis items comprise of thermal gravimetric analysis, weight yield, energy analysis, calorific value analysis, approximate analysis, and LCA were used to analyze the impact and benefit of the input and output. The microwave was set to operate for 30 minutes at 100 W to 400 W and 100 W to 350 W. The sludge mixing ratio used was 25 %, 50 %, and 75 %. The results showed that the sludge material measured by thermal gravimetric analysis (TGA) lost most of its weight at temperatures between 200 ° C to 500 ° C. As power increased, mass decreased. After the microwave power rose to 250 W, the remaining sludge was less than half of the raw material, and as low as 20.48 wt. % at 400 W. When the microwave power was at 100 W, the sludge mixing ratio increased from 0 % to 25 % and to 50 %, showing a strongly decreased, indicate that sludge co-torrefaction can improve the overall situation. In addition to the calorific value of the sludge produced is greater than the raw sludge at 100 W, remaining power options is less than raw materials. When the material of sludge ratio 25 % was at 100 W, the product property can be close with calorific value of the leucaena product, indicate that the product can retain the value of the property at low mixed ratio and low power. When the power was from 250 W to 400 W, the proportion of remaining volatile content was between 1.9 to 4.8 %, ash content was increased from 64.61 to 72.34 %, fixed carbon was between 30.63 to 25.74 % for the torrefied product of the sludge. The property of low-volatile bituminous coal was close to the ratio of H/C of the product at 300 W for the torrefied product of the sludge on the Van Krevelan Diagram. The product properties at 350 W and 150 W were close to the low volatile bituminous coal at sludge ratio 25 % and 50 %, respectively. In the life cycle assessment, the major costs of sludge were water content (85 %) up to 292 kWh in the oven-drying unit, indicate the water content of the sludge represents a significant indicator for sludge treatment. Sludge co-torrefaction can not only reduce drying costs but retain higher the calorific value.