|Abstract: ||本研究利用氣化處理技術探討下水污泥與工業區污水處理廠衍生之污泥(以下簡稱廢水污泥)，在控制當量比(equivalence ratio, ER)、氣化溫度(600~800℃)、廢水污泥摻混比例(0~60%)，以及蒸氣生質物比(Steam/Biomass, S/B) (0、0.5及1.0)等條件下，下水污泥與廢水污泥共同蒸氣氣化反應過程，合成氣及產氣組成特性、產物分佈特性、產能效率及重金屬排放分佈特性之影響。此外，本研究亦利用熱重-紅外線光譜儀，在改變不同升溫速率條件下，探討兩種污泥共同熱處理過程之反應動力，以及物種官能基之變化。|
根據熱重-紅外線光譜試驗分析結果可知，熱反應主要區分為三個階段，分別為200~400℃之纖維素/半纖維素分解階段，400~600℃木質素之分解階段，以及800~900℃之固定碳分解階段。其中裂解反應條件過程，主要由脫揮發、脫氫等反應，產生羰基、芳香族類，以及含O-H和C-H鍵之官能基產物。當反應條件改為二氧化碳之反應氣氛時，則會在第三階段發生Boudouard反應，氣相物種亦有C-O鍵結之官能基物種產生。至於以ER為0.3之空氣氣化反應條件時，除前述之物種外，氣相產物增加醚類及有機酸等物種之產生。反應活化能分析結果顯示，反應活化能隨廢水污泥比例增加而降低，其中裂解條件之反應活化能自44.5 kJ/mol降至22.1 kJ/mol，而反應條件改為二氧化碳及空氣氣化時，反應活化能則分別由37.7 kJ/mol及40.7 kJ/mol降至19.5 kJ/mol及19.1 kJ/mol，其說明增加廢水污泥比例，能使反應活化能降低，而氣化反應相較於裂解反應，亦較易將污泥轉化成氣相產物。
根據下水污泥與廢水污泥之共同氣化反應結果顯示，氣化反應溫度為800℃，廢水污泥比例由0%增加至40%時，合成氣之氫氣組成比例約自9.10 vol.%增加至12.46 vol.%，穩定階段之冷燃氣效率則由37.89 %增加至60.85 %。控制不同S/B及廢水污泥比例之條件下，隨著蒸氣量增加，有助於下水污泥及廢水污泥共同氣化之反應，其中穩定階段之冷燃氣效率最高可達60.85%。根據氣化產物之能量分佈特性結果顯示，產物能量分佈以氣體產物為主，約佔30~50%，而固體產物與液體產物之能量分佈比例皆小於10%。此外，氣化反應溫度為800℃，且控制不同廢水污泥添加比例與蒸氣生質物比之條件下，總能源回收效率約介於31.59~50.91%，同時，增加廢水污泥比例，能有效地提昇能源轉換效率。根據氣化產物之重金屬分佈特性結果可知，廢水污泥添加比例增加，固體殘餘物之Cu、Zn及Cr等重金屬含量亦隨之增加，至於重金屬Pb含量則呈現降低之現象，此與污泥之化學特性有關。此外，揮發溫度較高之金屬(如Cu、Cr等)，則主要分佈於固體產物。
整體而言，本研究不僅建立下水污泥與廢水污泥之基本特性分析與反應動力參數外，同時確認廢水污泥可作為下水污泥共同氣化之原料，提昇兩者污泥共同氣化產能效率之可行性。本研究具體之試驗分析結果，應可提供作為未來相關有機污泥廢棄物轉換能源應用技術之選擇參考依據。;This research investigates that evaluation on energy yields and metals partitioning characterization in co-gasification of sewage sludge (SS) and industrial wastewater sludge (IS) using fluidized bed gasifier with controlling temperature (600~800℃), IS ratio (0% to 60%), and steam-to-biomass ratio (S/B)(0 to 1.0).The functional group of gaseous speciation, thermal and kinetic characteristics in co-gasification of SS and IS by a thermal gravimetric analysis connected with a Fourier-transformed infrared spectrometer (TGA-FTIR) were also discussed.
The experimental results indicated that the thermal decomposition stages of tested sludge were including cellulose/semi-cellulose cracking stage (200~400℃), lignin decomposition stage (400~600℃), and fixed carbon volatilization stage (800~900℃) by TGA-FTIR. In the case of pyrolysis condition, the functional group of carbonyl, aromatic, O-H, and C-H were identified via devolatilization and dehydration reaction during thermal conversion process. When the CO2 used as reaction atmosphere, the functional group of C-O was identified in the gaseous products resulting in Boudouard reaction. In the case of gasification reaction (ER 0.3), the above functional groups were also identified in thermal conversion. However, the functional groups of ether and organic acid were extra speciation identified in the gaseous products. Based on the analysis results of pyrolysis condition, the activation energy was significantly decreased from 44.5 kJ/mol to 22.1 kJ/mol with IS addition ratio increasing from 0% to 100%. In the case of CO2 and air gasification, the activation energy was also decreased from 37.7 kJ/mol to 19.5 kJ/mol and from 40.7 kJ/mol to 19.1 kJ/mol with an increase in IS addition ratio, respectively. This is because the catalytic effect on the promotion of thermal reaction resulting in IS contains some Fe/Mn contents.
In the case of gasification temperature 800℃, the hydrogen production was increased from 9.1 vol. % to 12.46 vol.% with the IS addition ratio increasing from 0% to 40%. The cold gas efficiency (CGE) was significantly increased from 37.89% to 60.85%. Meanwhile, the energy conversion and CGE were increased with the steam-to-biomass ratio increasing. This is due to the steam will enhance the water gas reaction in the gasification process. Based on the energy distribution analysis results, the energy yield was approximately 30%~50% produced from gaseous products in co-gasification of tested sludge. In the case of gasification temperature 800℃, the total energy recovery rate was approximately ranged from 31.59% to 50.91%. By increasing IS addition ratio, it could enhance the total energy recovery rate in co-gasification. The metals partitioning results indicated that the Cu, Zn, and Cr were partitioned in solid phase with an increase in IS addition ratio. However, Pb partitioning percentage of solid phase was decreasing with IS addition ratio increasing. The metals partitioning characteristics were affected by sludge and metals physicochemical properties. In summary, the basic characterization of sewage sludge and industrial wastewater sludge and their kinetic parameters during thermal process were established, but also the confirmation on performance of industrial wastewater sludge used as co-gasification material and feasibility of improving energy yield. Therefore, the results of this study could provide the good information for energy conversion technologies selection of organic sludge waste.