木屑鍋爐之PCDD/Fs及dl-PCBs排放特性研究;Characterization of PCDD/Fs and dl-PCBs Emitted from Woodchip Boilers

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Title:	木屑鍋爐之PCDD/Fs及dl-PCBs排放特性研究;Characterization of PCDD/Fs and dl-PCBs Emitted from Woodchip Boilers
Authors:	白士庭;Bai, Shih-Ting
Contributors:	環境工程研究所
Keywords:	PCDD/Fs;dl-PCBs;木屑鍋爐
Date:	2017-01-23
Issue Date:	2017-05-05 17:44:05 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究探討北部兩座木屑鍋爐(簡稱為A廠及B廠)於不同操作模式對PCDD/Fs及dl-PCBs生成潛勢與排放特性之影響。A廠主要探討不同操作狀態(包含起爐、停爐及正常操作)對PCDD/Fs及dl-PCBs之影響，結果顯示因起爐為較差燃燒狀態，PCDD/Fs及dl-PCBs濃度(588.2 ng/Nm3)高於正常操作及停爐狀態；停爐狀態之PCDD/Fs及dl-PCBs濃度(41.05 ng/Nm3)則為三種操作狀態中最低，主因是木屑停止進料，缺少PCDD/Fs及dl-PCBs生成反應所需之碳源與氯源所致。B廠於不同操作模式(包含全載噴AC、全載未噴AC及半載噴AC)之測試結果顯示半載模式APCDs前PCDD/Fs及dl-PCBs濃度(113.6 ng/Nm3)較全載模式低(139.4 ng/Nm3)，主因為木屑進料量減半。活性碳可有效吸附氣相PCDD/Fs及dl-PCBs，有噴活性碳之氣相PCDD/Fs及dl-PCBs去除效率(95.60%及92.05%)皆高於未噴活性碳氣相PCDD/Fs及dl-PCBs去除效率(85.74%及79.76%)。在全載噴AC模式下，A廠APCDs前PCDD/Fs及dl-PCBs濃度皆高於B廠，顯示燃燒溫度會影響PCDD/Fs及dl-PCBs之生成潛勢，A廠爐體燃燒溫度(500-850 oC)較B廠(850-925 oC)低，易造成不完全燃燒反應，PCDD/Fs及dl-PCBs濃度相對較高。若以我國中小型焚化爐每小時四公噸以下的標準視之，A廠PCDD/Fs排放濃度於三種操作狀態皆超出法規標準；B廠則皆符合法規標準。木屑燃燒產生大量粒狀物，APCDs前煙道氣中粒狀物濃度相對較高，就氣/固相分布而言，A、B兩廠APCDs前PCDD/Fs皆以固相為主。不同條件之木屑燃燒，不會影響PCDD/Fs優勢物種分布，A、B兩廠APCDs前皆以1,2,3,4,6,7,8-H7CDF、1,2,3,4,6,7,8-H7CDD及O8CDD為優勢物種；dl-PCBs則受到進料組成及操作條件之影響，生成物種之分布有明顯差異。A、B兩廠BF飛灰戴奧辛類化合物濃度分別為979.2及406.2 ng/g。全載噴AC模式下A廠PCDD/Fs及dl-PCBs之去除效率分別為95.56%及88.63%；B廠PCDD/Fs及dl-PCBs之去除效率則分別為99.29%及94.94%。A廠PCDD/Fs及dl-PCBs之排放係數分別為17.24及1.120 μg WHO-TEQ/ton；B廠PCDD/Fs及dl-PCBs之排放係數則分別為1.520及0.1400 μg WHO-TEQ/ton。;This study characterizes the formation and emission of PCDD/Fs and dl-PCBs in two woodchips boilers during different operating periods. Two woodchips boilers (referred to as Plant A and B) investigated in this study are located in northern Taiwan. The sampling program of Plant A was conducted during different operating stages, including start-up, normal operation and shut-down periods. The results indicate that PCDD/F and dl-PCB concentrations (588.2 ng/Nm3) at APCDs inlet during the start-up period are much higher than those measured during normal operation and shut-down periods due to unstable combustion conditions. Concentrations of PCDD/F and dl-PCB (41.05 ng/Nm3) measured at APCDs inlet during the shut-down period were even lower than that measured during the normal operating period. It is due to the lack of carbon and chlorine sources since woodchip was not fed into the boiler during the shut-down period. The Plant B was investigated under three operating conditions, including full feed loading with injection of activated carbon, full feed loading without injection of activated carbon and half feed loading with injection of activated carbon. PCDD/Fs and dl-PCBs concentrations (113.6 ng/Nm3) measured at APCDs inlet during the half feed loading are lower than those measured during the full feed loading (139.4 ng/Nm3) due to the reduction of input woodchips. The removal efficiences of gas-phase PCDD/Fs and dl-PCBs achieved with ACI+BF are 95.60% and 92.05%, respectively, which are higher compared to the case without injection of activated carbon (85.74% and 79.76%, respectively). It demonstrates that gas-phase PCDD/Fs and dl-PCBs emissions can be effectively reduced by activated carbon injection. Durig full feed loading with the injection of activated carbon, PCDD/F and dl-PCB concentrations at APCDs inlet of the Plant A are significantly higher than those measured in the Plant B, due to the lower combustion temperature (500-850 oC) compared with Plant B (850-925 oC). Combustion condition remarkably affects PCDD/F and dl-PCB formation within the woodchip combustion process. The TEQ concentration of PCDD/Fs measured at the stack of the Plant A during different operating stages are significantly higher than the emission limit, while those of Plant B are lower than the regulation limit (0.5 ng I-TEQ/Nm3). For both Plants A and B, solid-phase PCDD/Fs dominate at APCDs inlet during different operating conditions because combustion of woodchips generates high concentration particulate matter. Different operating stages of woodchips combustion do not affect distributions of PCDD/F congeners significantly. Major PCDD/F congeners at APCDs inlet of Plants A and B during different periods include 1,2,3,4,6,7,8-HpCDF, 1,2,3,4,6,7,8-HpCDD and OCDD. The composition of feeding materials and different operating conditions affect the distributions of dl-PCB congeners. Concentrations of dioxin (PCDD/Fs+dl-PCBs) in the BF ash of Plants A and B during full feed loading with injection of activated carbon are measured 979.2 and 406.2 ng/g. Removal efficiencies of PCDD/Fs and dl-PCBs of the Plant A are 95.56% and 88.63%, respectively, while those of the Plant B are 99.29% and 94.94%. PCDD/Fs and PCBs emission factors of Plant A are 17.24 and 1.120 μg WHO-TEQ/ton, respectively. For the Plant B, the emission factors of PCDD/Fs and PCBs are 1.520 and 0.1400 μg WHO-TEQ/ton, respectively.
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