汽電共生設施重金屬污染物排放調查及管制策略研究

Investigation and Control Strategies of Heavy Metal Emissions from Cogeneration Power Facilities

周書瑋(Shu-Wei Chou)

指導教授 ： 席行正

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2013年)

https://doi.org/10.6841/NTUT.2013.00270

摘要

近年來，由於汽電共生技術之發展，國內部份工廠改為使用此技術，以提高能源之轉換效率；然而，如果汽電共生廠排放之污染物濃度超標，則會讓採用此技術之美意大打折扣，並造成環境問題。因此，本研究針對國內四座汽電共生廠，包含乙座都市廢棄物焚化爐（A廠）及三座燃煤鍋爐（B、C及D廠）進行重金屬污染物排放調查，並評估不同防制設備對於重金屬之去除效率。最後，根據調查之結果，研提可行之控制技術及未來管制策略之建議。本研究於各廠防制設備前及Stack兩點進行同步採樣，同時亦針對各廠投入物（燃料煤、製程水、廢輪胎、污泥、油灰及石灰石）以及產出物（飛灰、底灰及廢水），一併進行採樣分析。
研究結果顯示，非汞重金屬因多具有高沸點，於煙道中相當比例以固相型態存在，因此，採用高效率之除塵設備（ESP/FF）即可有效控制其排放，各廠對於非汞重金屬之去除效率均可達90%以上；然而，汞因高揮發之特性，主要以氣相型態存在，B、C廠因防制設備採用wFGD，因此，對具有高水溶性之Hg2+有顯著之去除效果；但是，因燃煤鍋爐尾氣特性為高SO2及低HCl濃度，此特性會抑制Hg0之氧化反應，故煙道中以低水溶性及低沸點之Hg0為主，使得B、C廠之總汞去除效率分別為78%及74%，明顯低於A廠之去除率（97%）。就排放係數而言，受測之非汞重金屬以Zn、Ni及Cu為較高；而對於汞而言，三座燃煤電廠因燃料較為單純，其汞排放係數（10.3－16.3 mg ton-coal-1）均低於A廠（28.0 mg ton-solid-1）。就三座燃煤鍋爐之流布來看，非汞重金屬以飛灰（>90%）為主，其次為底灰（5－10%），於Stack排放比例則較低（<5%）；對於汞而言，以飛灰（62－73%）為主，其次為Stack排放（26－38%）及廢水（5－10%），最低則為底灰（0.08－0.56%）。
各廠所排放重金屬濃度均符合現行之法規標準，但為了因應後續可能加嚴之法規，以廢棄物為燃料時，防制設備建議可使用SCR/SNCR+SDA+(改質)ACI+FF之流程；以煤炭為燃料時，建議以SCR+FF/ESP+wFGD之流程，如有添加副燃料之情況，則需視實際情況規劃。

關鍵字

汽電共生 ； 燃煤 ； 重金屬 ； 流布 ； 排放係數 ； 空氣污染控制設備

並列摘要

Recently, in order to enhance the overall energy efficiency, a part of domestic factories have changed to use the cogeneration system. Cogeneration system can reduce not only fuel cost but also waste gas emissions. However, emissions from cogeneration plants are still a concern to the public. This study selected four cogeneration plants, including one municipal waste incinerator (MWI, Plant A) and three coal-fired power plants (CFPPs, Plants B, C and D) to investigate the emission and distribution of heavy metals. Sampling and analysis of all the inputs and outputs in the plant were conducted to obtain the heavy metal distribution, mass balance, emission characteristics, and removal efficiency of the air pollution control devices (APCDs).
The results indicated that heavy metals except mercury in the flue gas were mainly existed in solid phase, because of the high boiling points. Highly efficient particle control devices such as ESP or FF can effectively control their emissions. Its for non-mercury heavy metals the removal efficiency can reach ≧90%. In contrast, mercury mainly exist in the gas phase due to high volatility boiling point：357℃) presents, which cause Hg difficult to remove, and discharge to the atmosphere. The Hg2+ is water soluble and can be removed by wet scrubber. Plant B and C have wFGD as an APCDs, therefore they had significant removal for Hg2+. Because a great Hg0 proportion is the flue gas of plants B and C, the the overall Hg removal efficiencies of plants B and C were 78% and 74%, respectively, which were lower than plant A (SDA+ACI+FF) that had 97% removal efficiency. The Hg emission concentration of Plants A, B, C, and D were 4.09, 1.74, 2.31, and 1.49 μg Nm-3, respectively. In addition, the calculated emission factors for CFPPs plant B, C, and D were within 10.3－16.3 mg ton-coal-1 compared to 28.0 mg ton-solid-1 for MWI plant A. These results indicate that further improvement is needed for the present municipal waste recycle system of Taiwan. The distribution of CFPPs for non-mercury metals, the major output was attributed to fly ash (>90%), followed by the bottom ash (5－10%) and <1% was emitted from the stack. For mercury, 62－73% was in fly ash and 5－10% retained in the FGD effluent water, and 26－38% was discharged from the stack.
For enhancing the pollution removal capability by APCDs, some APCDs processes are suggested in this study. For MWIs, “SCR/SNCR+SDA+modified-ACI+FF” are suggested. For Cogeneration plants burning coal, “SCR+FF/ESP+wFGD” are suggested. However, if blend fuels are used the APCDs process may have to be altered based on the real situtations.

並列關鍵字

Cogeneration ； Coal combustion ； Heavy metal ； Heavy metal distribution ； Emission factor ； APCDs

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