| 摘要: | 本研究利用固定床及流體化床氣化系統探討廢車破碎殘餘物(Automobile shredder residue, ASR)，在控制當量比(Equivalene ratio, ER)、氣化溫度(900 ℃)及催化劑添加(5~15 wt.%)之條件下，評估產氣組成特性、產物分佈特性、產能效率及污染物(重金屬、硫及氯)排放特性，其中催化劑係以廢棄牡蠣殼自行製備，相關催化劑之功能特性，亦是本研究探討之重點。
牡蠣殼為本研究選擇製備催化劑之重要基材，其中牡蠣殼經破碎為粉末後，經熱重及元素分析分析結果顯示，粉末牡蠣殼之主要組成為90.55~96.86 wt.%之碳酸鈣，其比表面積約為1.983 m2/g，本研究將粉末牡犡殼視為一種催化劑(催化劑A)。另將前述之粉末牡犡殼經800℃煅燒3小時後，製備為煅燒牡蠣殼(催化劑B)，經試驗分析結果可知，主要組成為氧化鈣，其比表面積略增為4.932 m2/g。另以氫氧化鈉之化學方法製備之催化劑C，主要成分為氫氧化鈣，其比表面積與原粉末牡蠣殼相似，約為1.978 m2/g。
根據氣體組成及產能效率分析結果顯示，固定床催化氣化反應系統，在無添加催化劑條件下，氣體熱值及冷燃氣效率分別約為1.55 MJ/Nm3及5.22 %。隨著添加前述自製催化劑，ASR轉換之產能效率則有增加之現象，以添加10 wt.%之自製催化劑條件，氣體熱值自無催化劑之1.55 MJ/Nm3分別增加至3.11 MJ/Nm3(催化劑A)、3.06 MJ/Nm3(催化劑B)及2.67 MJ/Nm3(催化劑C)。另以煅燒牡犡殼粉末(催化劑B)而言，冷燃氣效率亦由5.22 %增加至11.50 %。整體而言，添加催化劑A之試驗結果有最高之氣體熱值及冷燃氣效率，此係因催化劑A具有較高之比表面積，可促進甲烷生成反應，明顯提昇氣體熱值及冷燃氣效率。至於流體化床之試驗結果顯示，以添加催化劑A及10 wt.%比例條件為例，氣體熱值及冷燃氣效率分別約為3.80 MJ/Nm3及25.29 %。依能源轉換效率而言，流體化床氣化反應系統，具有較佳之ASR轉換能源之效率。
重金屬排放特性之分析結果顯示，以添加10 wt.%催化劑A及固定床氣化反應系統而言，重金屬鉻、銅及鋅之分佈特性，因其揮發溫度較高，主要以分佈於焦碳為主，分別約佔97.54 %、85.74 %及90.07 %。重金屬鎘及鉛之分佈，則因其具有較高之揮發性，故以焦油或粒狀物為主要分佈地點，分別約佔57.09 %及65.77 %。至於重金屬汞則因其具有高揮發性，主要以合成氣為其分佈地點，約占87.24 %。至於以流體化床氣化爐為反應系統，重金屬分佈特性之變化，主要受到流體化床混合攪動特性之影響，可能發生粒狀物傳曳作用，使得污染物分佈至粒狀物，其中以重金屬鉛之分佈特性變化最為明顯。整體而言，本研究初步結果可知，自製催化劑可明顯促進ASR氣化轉換能源之效率，同時對於ASR氣化處理過程，重金屬及其衍生污染物之排放及分佈特性，亦有完整的評估與探討，因此，研究成果可作為未來ASR氣化處理過程之技術選擇及重金屬排放與管制策略之參考依據。
;This study investigates that automobile shredder residue (ASR) converted into energy by fixed bed and fluidized bed gasification system with controlling at ER 0.2, temperature 900℃ and 5-15 wt.% prepared catalyst addition. The producer gas composition, products distribution, energy yield efficiency and trace pollutants (e.g. heavy metal, sulfur and chlorine) emission characteristics were also evaluated. The tested catalysts were prepared by oyster shell and their performances were discussed.
The waste oyster shell was a major matrix for manufacturing prepared catalyst. Catalyst A was directly converted from waste oyster shell to powder oyster shell via shredding. Based on the analysis results of elemental and thermogravimetric analysis, the powder oyster shell (Catalyst A) was approximately 90.55-96.86 wt.% of calcium carbonate with 1.983 m2/g of specific surface area. Catalyst B was manufactured from powder oyster shell calcined at 800℃ for 3 hours (referred as calcined oyster shell). The major composition of tested catalyst B was calcium oxide. The specific surface area was slightly increased to 4.932 m2/g. The Catalyst C was prepared by the chemical method adding sodium hydroxide and expected to form calcium hydroxide. The specific surface area of tested Catalyst C was approximately 1.978 m2/g that it was similar with that of tested catalyst A.
In the case of fixed bed gasifier and without tested catalyst addition, the heating value of producer gas and cold gas efficiency (CGE) were approximately 1.55 MJ/Nm3 and 5.22%, respectively. And the energy yield efficiency of ASR conversion was increased with an increase in tested prepared catalyst addition. In the case of 10 wt.% of tested prepared catalysts addition, the producer gas heating value increased from 1.55 MJ/Nm3 to 3.11 MJ/Nm3 (catalyst A), 3.06 MJ/Nm3 (catalyst B), and 2.67 MJ/Nm3 (catalyst C), respectively. Meanwhile, in the case of 10 wt% tested catalyst B addition, CGE was also increased from 5.22 % to 11.50 %. Overall, the prepared Catalyst A could enhance heating value and CGE resulted in high specific surface area and promotion in methane formation reaction. On the other hand, in the case of fluidized bed gasifier and 10 wt.% Catalyst A addition, the producer gas heating value and CGE were approximately 3.80 MJ/Nm3 and 25.29 %, respectively. In terms of energy conversion efficiency, the fluidized bed gasification system has better ASR energy conversion efficiency than that of fixed bed gasifier.
The heavy metals emission characteristics results indicated that chromium, copper and zinc were mainly partitioned in char under gasified by fixed bed gasifier and 10 wt.% Catalyst A addition. The Cr, Cu, and Zn partitioning percentages of char were approximately 97.54%, 85.74% and 90.07%, respectively. This is because the above tested metals have a higher volatilization temperature. The partitioning of cadmium and lead were mainly partitioned in tar or particulate resulted in their high volatility characteristics. The Cd and Pb partitioning percentages of tar and/or particulate were approximately 57.09% and 65.77%, respectively. In the case of mercury partitioning characteristics, the Hg partitioning percentage of syngas was nearly 87.24% resulted in Hg has a relatively high volatility. As for the fluidized bed gasifier system, the variation of the heavy metals partitioning characteristics was mainly influenced by the turbulent characteristics of the fluidized bed gasifier. Therefore, the most tested metals were mainly partitioned in particulate, especially for Pb partitioning characteristics was significantly varied. In summary, the prepared catalysts used in this research could enhance energy conversion from ASR via gasification. Meanwhile, the tested heavy metals emission and partitioning characteristics were also well established during ASR gasification process. Therefore, the results of this research could provide the good information for selection of gasification technologies and control strategies of metals emission in the future. |
