科學園區廢水廠污泥氣化產能效率及重金屬排放特性之研究;Characterization of energy yield and heavy metal emission in gasification of sludge derived from science park wastewater treatment plant

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Title:	科學園區廢水廠污泥氣化產能效率及重金屬排放特性之研究;Characterization of energy yield and heavy metal emission in gasification of sludge derived from science park wastewater treatment plant
Authors:	賴姿伃;Lai, Tzu-Yu
Contributors:	環境工程研究所
Keywords:	污泥;催化氣化;白雲石;橄欖石;金屬分布;Sludge;Catalytic gasification;Dolomite;Olivine;Metal partitioning
Date:	2024-01-12
Issue Date:	2024-03-05 17:59:18 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究主要探討科學園區廢水處理廠衍生污泥，氣化處理轉換產能之可行性，實驗分別控制氣化溫度(700~900℃)及添加不同比例(5%、10%、15%)白雲石及橄欖石作為礦石催化劑之條件，探討污泥產氣組成及產能效率之影響，同時評估污泥所含微量重金屬之排放特性，此外，研究亦針對添加橄欖石催化劑之重複利用性，進行試驗與評估。氣化試驗結果顯示，氣化溫度由700℃增加至900℃時，主要產氣階段(5~16分鐘)之氫氣與一氧化碳產生比例，分別由5.27 vol.%及2.42 vol.%增加至11.38 vol.%及12.58 vol.%，產氣平均熱值由2.00 MJ/Nm3增加至6.14 MJ/Nm3，此係提高氣化溫度助於促進水氣及Boudouard等吸熱反應。添加白雲石及橄欖石作為礦石催化劑之試驗結果顯示，操作溫度為900℃時，添加10%白雲石試驗，主要產氣階段氫氣與一氧化碳組成比例，分別為13.32 vol.%及11.44 vol.%，而平均氣體熱值為6.15 MJ/Nm3。當添加5%橄欖石試驗，主要產氣階段氫氣與一氧化碳之組成比例，分別為10.73 vol.%及13.77 vol.%，此時平均氣體熱值為5.04 MJ/Nm3，整體而言，以白雲石作為礦石催化劑時，其催化效果使氣體產量及熱值明顯高於高溫氣化及添加橄欖石。此外，添加經三次回收之5%橄欖石試驗結果顯示，主要產氣階段氫氣與一氧化碳組成比例，分別介於12.48 vol.%~15.43 vol.%及6.63 vol.%~11.98 vol.%之間，且平均氣體熱值約為5.18 MJ/Nm3，上述所得數值均高於未回收狀態之5%橄欖石試驗結果，說明橄欖石經回收後，其催化效果優於新鮮橄欖石且具重複利用性。重金屬排放特性及其物種模擬分析結果顯示，提升氣化溫度後，Zn之固相分布比例由77.25%增加至82.10%；添加白雲石與橄欖石後，分布比例分別由72.30%及86.27%增加至74.70%及90.27%，此係白雲石中CaO具吸附作用，且橄欖石中Fe2O3及SiO2分別以ZnFe2O4(s)、ZnSiO3(s)形式結晶所致；對5%橄欖石進行回收後，其分布比例則由91.49%增加至97.90%，說明橄欖石經回收後同時具備吸附及結晶方式捕捉金屬Zn。此外，特殊重金屬Mo、In及Ga在所有操作條件下，僅有In之固相分布比例，隨氣化溫度增加，由61.11%下降至25.03%，說明操作溫度對重金屬In有較顯著的影響。整體而言，根據本研究成果已初步驗證，科學園區廢水污泥具氣化處理可行性，添加礦石催化劑後，可進一步提升氣體產量及熱值，其中橄欖石具重複利用之可行性，此外，本研究亦探討科學園區廢水污泥於氣化處理過程中，各類金屬元素之排放特性與物種模擬，因此，研究成果未來可提供相關廢水處理廠，針對其產生之衍生污泥，應用於此能源轉換技術，及處理過程中金屬元素排放控制之參考依據。 ;This research investigated the feasibility of energy conversion of sludge derived from the Science Park wastewater treatment plant by gasification. The experimental conditions were designed to controll gasification temperatures (700~900℃) and add different proportions (5%, 10%, 15%) of dolomite and olivine as mineral catalysts. This research aimed to study the effect on produced gas composition and energy production efficiency and evaluate the trace metals emission characteristics during sludge gasification. Meanwhile, the study was also conducted to assess the reusability of olivine catalysts. Experimental results indicate that the hydrogen and carbon monoxide compositions increased from 5.27 vol.% and 2.42 vol.% to 11.38 vol.% and 12.58 vol.% with the temperature increasing from 700℃ to 900℃ during the major gas production phase (5~16 minutes), respectively. The average heating value of the produced gas increased significantly from 2.00 MJ/Nm3 to 6.14 MJ/Nm3. This is because higher gasification temperatures facilitate water gas and Boudouard reactions. Examining the effect of dolomite and olivine as mineral catalysts at 900℃,it was observed that the 10% dolomite addition resulted in hydrogen and carbon monoxide compositions of 13.32 vol.% and 11.44 vol.%, corresponding with an average gas heating value of 6.15 MJ/Nm3. Conversely, using 5% olivine yielded 10.73 vol.% for hydrogen and 13.77 vol.% for carbon monoxide, with an average gas heating value of 5.04 MJ/Nm3. In summary, dolomite proved to be a superior catalyst, significantly increasing produced gas yield and heating value compared to high-temperature gasification and the olivine addition. Furthermore, experiments involving the reuse of 5% olivine after three cycles demonstrated improved catalytic effects. The produced gas compositions were 12.48 vol.%~15.43 vol.% for hydrogen and 6.63 vol.%~11.98 vol.% for carbon monoxide, respectively. The average heating value of the produced gas was approximately 5.18 MJ/Nm3, higher than that of fresh olivines. It implied that the reused olivine could provide a superior catalytic performance after the recycling experiment. According to the results of heavy metal emission characteristics and speciation simulation, the solid-phase partitioning percentage of Zn was increased from 77.25% to 82.10% with the increase in gasification temperature. However, in the case of dolomite and olivine addition, the Zn solid-phase partitioning percentage was increased from 72.30% and 86.27% to 74.70% and 90.27%, respectively. This is because dolomite and olivine containing CaO could adsorb the gas-phase Zn and the crystallization of ZnFe2O4(s) and ZnSiO3(s) facilitated by olivine containing Fe2O3 and SiO2. Regarding the olivine recyclability results, 5% reused olivine as a catalyst could also provide good Zn adsorption performance due to the adsorption and crystallization mechanism. The Zn solid-phase partitioning percentage was increased from 91.49% to 97.90%. Additionally, special heavy metals Mo, In, and Ga derived from sludge emission characteristics showed insignificant variations in solid-phase partitioning percentage with increased gasification temperatures. Except for In, the solid-phase partitioning percentage was decreased from 61.11% to 25.03% with an increase in temperature. It implied that In emissions could be significantly influenced by the gasification temperature. In conclusion, the gasification of sludge derived from Science park′s wastewater treatment plant is feasible, and this research confirms it. The addition of tested mineral catalysts enhances produced gas yield and heating value, and the tested olivine exhibited promising recyclability. The study also investigates the emission characteristics of various metals during the gasification process, providing valuable insights for Science Park wastewater treatment plants regarding the strategy selection for sludge utilization in energy conversion techniques and controlling metal emissions.
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