氮氧化物吸收程序操作參數研究

Pilot Study for Two-stage NOx Absorption process

周冠瑋(Kuan-Wei Chou)

指導教授 ： 陳俊成

淡江大學/工學院/水資源及環境工程學系碩士班/碩士(2013年)

https://doi.org/10.6846/TKU.2013.01124

摘要

光化學煙霧的前驅物質與形成酸雨的主要因素皆為NOx，因此氮氧化物處理技術的研發已成為必要的趨勢。然而，業界目前大多以選擇性觸媒還原法（SCR）及選擇性非觸媒還原法（SNCR）乾式處理法處理氮氧化物。大部分的氮氧化物控制技術，其處理設備大多是針對單一污染物所設計的，若要同時處理不同之污染物，則需建置另一套系統。故本研究則採用能針對多種污染物的濕式洗滌塔進行NOx的吸收。
本研究利用小型兩段式溼式洗滌塔對NOx進行有效率的去除。利用NO2高水溶性之特性，第一段以次氯酸鈉（NaClO）水溶液做為氧化劑，將NO氧化轉化成NO2，洗滌液中過飽和之NO2以氣體形式繼續導入第二段，以亞硫酸鈉（Na2SO3）水溶液做為還原劑，將NO2還原至N2，形成完整的氮氧化物吸收系統。
本研究結果歸納如下：
(1) 液體質量流率愈高，液體噴灑面積大，液氣接觸面積增加，NO轉化率（NO2去除率）隨之增加。
(2) 小型洗滌塔體積較小，氣體於塔內擴散均勻，因此氣體質量流率之影響不大。
(3) 相同液氣比，不同氣體質量流率，NO轉化率（NO2去除率）會因操作限值受限於洗滌塔體積，導致在較低的氣體質量率操作下，NO轉化率（ NO2去除率）較好。
(4) 當氧化段測得ORP值低於1050 mV、還原段測得高於-40 mV時， NO轉化率（NO2去除率）低於80％，需添加新的洗滌液進入，以維持其洗滌效果。
(5) 當氧化段測得pH值高於6時，需以硫酸調整pH值至5±0.5，使其優勢物種保持為HOCl；當測得pH值低於8.3時，需加入氫氧化鈉調整pH值至9以上，維持其還原效果。
(6) 氧化段效果良好，但經過還原段洗滌後，NO再次生成，且與入口NO濃度幾乎相同，因氧化段部分氯氣生成的氧化劑與還原劑效果抵銷，使NO2溶於水中形成的亞硝酸再次分解出NO。

關鍵字

洗滌塔 ； 氮氧化物 ； NO轉化率 ； NO2去除率

並列摘要

In this study, a lab-scale two-stage wet scrubber for NOx removal was tested. In the first stage a sodium hypochlorite (NaClO) solution was used as the oxidant to convert NO into more soluble NO2. In the second stage,a sodium sulfite (Na2SO3) solution was used as a reducing agentto reduce NO2into N2. The tested results were compared with results from a pilot test. This study concluded the following findings:
1. The higher liquid mass rate and liquid-gas contact area result in the higher NOconversion rate andNO2 reduction rate.
2. The gas mass rate has little effect on the NO conversion and NO2 reduction rate in the lab-scale scrubber tests because thespreading of gas are very even within the column.
3. With the same liquid-gas ratio, the NO conversion and NO2 reduction rateare limited by the volume of the scrubbing tower, therefore lower gas mass rate results in higher NO conversion orNO2 reduction rate.
4. When the measured ORP is less than 1050 mV in the oxidation stage, or more than -40 mVin the reduction stage a new oxidant or reducing agents needs to be added into thescrubbingsolution to maintain required NOX treatment.
5. When the measured pH in the oxidation section is over pH 6, sulfuric acid was added to adjust the pH to5 ± 0.5 to keep HOCl as the dominant species in the scrubbing solution; when the measured pH is below 8.3 in the reduction section, sodium hydroxide is added to adjust the pH over pH 9 to maintain reduction capability of the reducing solution.
6. In the oxidation-reduction sequential test, In the oxidation stage, conversion of NO into NO2 is high in the oxidation stage, but after reduction stage NO is re-generated and the NO concentration is almost the same as the inlet. It is believed that part of oxidizing chlorine generated in the oxidation stage offsets reducing agent in the reduction section and interfere the mechanisms of NO2 reduction system that results in more NO2 reduction to NO than to N2.

並列關鍵字

scrubber ； nitrogen oxides ； NO conversion rate ； NO2 reduction rate

參考文獻

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