基于电解海水的模拟船舶废气脱硝试验
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摘要
基于试验级别喷淋反应器,研究电解海水用于船舶废气脱硝的原理可行性。考察电解制备有效氯浓度、初始pH值、NO入口浓度及洗涤运行模式对脱硝性能的影响。试验结果表明:对于非循环喷淋,随着有效氯浓度升高,NO_x脱除率均迅速上升,但当有效氯浓度超过一定值后,脱除率增速变缓。电解溶液pH值对NO脱除率有明显影响,相同有效氯浓度条件下,电解海水初始pH值=7比默认pH值≈8的脱硝效果更好。当NO初始体积浓度从0.025%变化到0.125%时,NO脱除率从19%增长到80%,而NO_x脱除率从14%增长到63%。适当提高有效氯浓度与NO入口浓度,并维持溶液pH值≈7,将是提升电解海水法脱硝效果的有效途径,且脱硝效果将有望满足MARPOL公约附则VI Tier III标准。此外,循环喷淋结果表明,初始20 min内,NO_x脱除率及溶液pH值分别保持49%和6.5以上,占整个循环时间的74%,说明电解海水在闭式循环模式下脱硝持续性较好。
The feasibility of the principle that controls marine NO_x emissions through electrolyzed seawater scrubbing is evaluated with a lab-scale scrubber. The relation between the NO_x removal efficiency and the factors, such as concentration of electrolysis-generated chlorine, initial pH value of seawater, NO_x inlet concentration as well as operating mode of scrubbing is investigated individually. For once-through mode, the NO conversion efficiency and NO_x removal efficiency increased sharply as the electrolysis-generated chlorine concentration goes up, but when the concentration exceeds a certain value, the rates become slightly lower. The pH value of seawater has a significant impact on NO conversion efficiency. NO conversion efficiency at pH 7 are substantially higher than that without pH control around pH 8 under same oxidant concentration. When the NO inlet concentration varies from 0.025% to 0.125%, NO conversion efficiency goes up from 19% to 80% and the NO_x removal efficiency from 14% to 63%. The experiments indicate that there are several effective measures to improve the scrubbing performance, including increasing both electrolysis-generated chlorine concentration and NO inlet concentration and maintaining pH value of the solution at approximately 7. In recirculating scrubbing mode, the experiments show that both the NO_x removal efficiency and the pH of seawater are kept above 49% and 6.5 respectively during the initial 20 min, which accounts for 74% of the circulation time, suggesting the fitness of the electrolyzing seawater scrubbing for closed loop operation. The conclusion is that the method possesses the potential to meet the Tier III requirement of MARPOL Annex VI.
The feasibility of the principle that controls marine NO_x emissions through electrolyzed seawater scrubbing is evaluated with a lab-scale scrubber. The relation between the NO_x removal efficiency and the factors, such as concentration of electrolysis-generated chlorine, initial pH value of seawater, NO_x inlet concentration as well as operating mode of scrubbing is investigated individually. For once-through mode, the NO conversion efficiency and NO_x removal efficiency increased sharply as the electrolysis-generated chlorine concentration goes up, but when the concentration exceeds a certain value, the rates become slightly lower. The pH value of seawater has a significant impact on NO conversion efficiency. NO conversion efficiency at pH 7 are substantially higher than that without pH control around pH 8 under same oxidant concentration. When the NO inlet concentration varies from 0.025% to 0.125%, NO conversion efficiency goes up from 19% to 80% and the NO_x removal efficiency from 14% to 63%. The experiments indicate that there are several effective measures to improve the scrubbing performance, including increasing both electrolysis-generated chlorine concentration and NO inlet concentration and maintaining pH value of the solution at approximately 7. In recirculating scrubbing mode, the experiments show that both the NO_x removal efficiency and the pH of seawater are kept above 49% and 6.5 respectively during the initial 20 min, which accounts for 74% of the circulation time, suggesting the fitness of the electrolyzing seawater scrubbing for closed loop operation. The conclusion is that the method possesses the potential to meet the Tier III requirement of MARPOL Annex VI.
引文
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[14] GUO R,PAN W,ZHANG X,et al.The Absorption Kinetics of NO into Weakly Acidic NaClO Solution [J].Separation Science and Technology,2013,48(18):2871-2875.
[15] RAGHUNATH C V,MONDAL M K.Reactive Absorption of NO and SO2 into Aqueous NaClO in a Counter-Current Spray Column [J].Asia-Pacific Journal of Chemical Engineering,2016,11(1):88-97.
[16] EIMANHARAWY S,HAFEZ A.Study of Seawater Alkalization as a Promising RO Pretreatment Method [J].Desalination,2003,153(1):109-120.
[2] DESHWAL BR,LEE SH,JUNG JH,et al.Study on the Removal of NOx from Simulated Flue Gas Using Acidic NaClO2 Solution [J].Journal of Environmental Sciences,2008,20(1):33-38.
[3] LIU Y,ZHANG J,SHENG C.Kinetic Model of NO Removal from SO2-Containing Simulated Flue Gas by Wet UV/H2O2 Advanced Oxidation Process [J].Chemical Engineering Journal,2011,168(1):183-189.
[4] ZHOU S,ZHOU J,FENG Y,et al.Marine Emission Pollution Abatement Using Ozone Oxidation by a Wet Scrubbing Method [J].Industrial & Engineering Chemistry Research,2016,55(20):5825-5831.
[5] AN S,NISHIDA O.New Application of Seawater and Electrolyzed Seawater in Air Pollution Control of Marine Diesel Engine [J].JSME International Journal Series B Fluids and Thermal Engineering,2003,46(1):206-213.
[6] NISHIDA O,HOSODA S,ADACHI K,et al.Removing Method of Marine NOx by Seawater Electrolysis [J].Review of the Faculty of Maritime Sciences,Kobe University,2004,1:75-82.
[7] MORRIS JC.The Acid Ionization Constant of HOCl from 5° to 35° [J].Journal of Physical Chemistry,1966,70(12):3798-3805.
[8] GHIBAUDI E,BARKER JR,BENSON SW.Reaction of NO with Hypochlorous Acid [J].International Journal of Chemical Kinetics,2010,11(8):843-851.
[9] KOBAYASHI H,TAKEZAWA N,NIKI T.Removal of Nitrogen Oxides with Aqueous Solutions of Inorganic and Organic Reagents [J].Environmental Science & Technology,1977,11(2):190-192.
[10] CHISWELL B,O’HALLORAN KR.Use of Lissamine Green B as a Spectrophotometric Reagent for the Determination of Low Residuals of Chlorine Dioxide [J].Analyst,1991,116(6):657-661.
[11] LIU Y,ZHANG J,XIE F,et al.Study on Enhancement Mechanism of NO Absorption in K2FeO4 Solution Basing on Mass Transfer-Reaction Theory [J].Chemical Engineering Research and Design,2016,111:196-203.
[12] 张成芳.气液反应和反应器[M].北京:化学工业出版社,1985:19-46.
[13] CHEN L,HSU C H,YANG C L.Oxidation and Absorption of Nitric Oxide in a Packed Tower with Sodium Hypochlorite Aqueous Solutions [J].Environmental Progress & Sustainable Energy,2010,24(3):279-288.
[14] GUO R,PAN W,ZHANG X,et al.The Absorption Kinetics of NO into Weakly Acidic NaClO Solution [J].Separation Science and Technology,2013,48(18):2871-2875.
[15] RAGHUNATH C V,MONDAL M K.Reactive Absorption of NO and SO2 into Aqueous NaClO in a Counter-Current Spray Column [J].Asia-Pacific Journal of Chemical Engineering,2016,11(1):88-97.
[16] EIMANHARAWY S,HAFEZ A.Study of Seawater Alkalization as a Promising RO Pretreatment Method [J].Desalination,2003,153(1):109-120.
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