光谱学与光谱分析
光譜學與光譜分析
광보학여광보분석
SPECTROSCOPY AND SPECTRAL ANALYSIS
2015年
6期
1639-1642
,共4页
张立芳%王飞%俞李斌%严建华%岑可法
張立芳%王飛%俞李斌%嚴建華%岑可法
장립방%왕비%유리빈%엄건화%잠가법
可调谐激光吸收光谱%近红外%NH3浓度测量%探测极限
可調諧激光吸收光譜%近紅外%NH3濃度測量%探測極限
가조해격광흡수광보%근홍외%NH3농도측량%탐측겁한
Tunable diode laser absorption spectroscopy%Near-infrared%Ammonia concentration measurement%Detection limit
为了对电厂脱硝过程中逃逸的微量氨气进行在线检测,实验室采用可调谐激光吸收光谱技术对常温常压下以及不同温度下的低浓度氨气进行了测量试验,其中电厂逃逸氨气检测处温度约为650 K。通过分析近红外波段的氨气吸收谱线,并考虑实际测量环境H2 O和CO2等浓度很大的气体吸收谱线的干扰,实验选取2.25μm附近的ν2+ν3谱线作为浓度检测谱线。为了验证所选谱线对低浓度N H3的测量能力,实验对H2 O ,CO2和N H3的吸收谱线进行模拟,发现低浓度N H3受较大浓度的H2 O和CO2谱线的干扰较小,尤其是CO2谱线的干扰可以忽略不计,且2.25μm处谱线强度远远大于通讯波段1.53μm处的谱线。基于新型Herriott池以及高温管式炉,结合可调谐激光吸收光谱中的直接吸收技术和波长调制技术,实现了对不同温度下超低浓度N H3的高分辨率快速检测。常温常压下其线型函数可以利用洛伦兹线型来近似描述,直接吸收测量技术可以使探测极限降低到0.225×10-6。通过采用简单降噪处理技术如多次平均、简单小波分析等,得到不同温度下的谐波信号与浓度具有良好的线性关系,为采用可调谐激光吸收光谱技术进行现场低浓度逃逸氨气检测提供了很好的依据。
為瞭對電廠脫硝過程中逃逸的微量氨氣進行在線檢測,實驗室採用可調諧激光吸收光譜技術對常溫常壓下以及不同溫度下的低濃度氨氣進行瞭測量試驗,其中電廠逃逸氨氣檢測處溫度約為650 K。通過分析近紅外波段的氨氣吸收譜線,併攷慮實際測量環境H2 O和CO2等濃度很大的氣體吸收譜線的榦擾,實驗選取2.25μm附近的ν2+ν3譜線作為濃度檢測譜線。為瞭驗證所選譜線對低濃度N H3的測量能力,實驗對H2 O ,CO2和N H3的吸收譜線進行模擬,髮現低濃度N H3受較大濃度的H2 O和CO2譜線的榦擾較小,尤其是CO2譜線的榦擾可以忽略不計,且2.25μm處譜線彊度遠遠大于通訊波段1.53μm處的譜線。基于新型Herriott池以及高溫管式爐,結閤可調諧激光吸收光譜中的直接吸收技術和波長調製技術,實現瞭對不同溫度下超低濃度N H3的高分辨率快速檢測。常溫常壓下其線型函數可以利用洛倫玆線型來近似描述,直接吸收測量技術可以使探測極限降低到0.225×10-6。通過採用簡單降譟處理技術如多次平均、簡單小波分析等,得到不同溫度下的諧波信號與濃度具有良好的線性關繫,為採用可調諧激光吸收光譜技術進行現場低濃度逃逸氨氣檢測提供瞭很好的依據。
위료대전엄탈초과정중도일적미량안기진행재선검측,실험실채용가조해격광흡수광보기술대상온상압하이급불동온도하적저농도안기진행료측량시험,기중전엄도일안기검측처온도약위650 K。통과분석근홍외파단적안기흡수보선,병고필실제측량배경H2 O화CO2등농도흔대적기체흡수보선적간우,실험선취2.25μm부근적ν2+ν3보선작위농도검측보선。위료험증소선보선대저농도N H3적측량능력,실험대H2 O ,CO2화N H3적흡수보선진행모의,발현저농도N H3수교대농도적H2 O화CO2보선적간우교소,우기시CO2보선적간우가이홀략불계,차2.25μm처보선강도원원대우통신파단1.53μm처적보선。기우신형Herriott지이급고온관식로,결합가조해격광흡수광보중적직접흡수기술화파장조제기술,실현료대불동온도하초저농도N H3적고분변솔쾌속검측。상온상압하기선형함수가이이용락륜자선형래근사묘술,직접흡수측량기술가이사탐측겁한강저도0.225×10-6。통과채용간단강조처리기술여다차평균、간단소파분석등,득도불동온도하적해파신호여농도구유량호적선성관계,위채용가조해격광흡수광보기술진행현장저농도도일안기검측제공료흔호적의거。
In order to on‐line measure the trace ammonia slip of the commercial power plant in the future ,this research seeks to measure the trace ammonia by using tunable diode laser absorption spectroscopy under ambient temperature and pressure ,and at different temperatures ,and the measuring temperature is about 650 K in the power plant .In recent years lasers have become commercially available in the near‐infrared where the transitions are much stronger ,and ammonia’s spectroscopy is pretty com‐plicated and the overlapping lines are difficult to resolve .A group of ammonia transitions near 4 433.5 cm-1 in theν2 +ν3 combi‐nation band have been thoroughly selected for detecting lower concentration by analyzing its absorption characteristic and consid‐ering other absorption interference in combustion gases where H2O and CO2 mole fraction are very large .To illustrate the poten‐tial for NH3 concentration measurements ,predictions for NH3 ,H2O and CO2 are simultaneously simulated ,NH3 absorption lines near 4 433.5 cm-1 wavelength meet weaker H2O absorption than the commercial NH3 lines ,and there is almost no CO2 ab‐sorption ,all the parameters are based on the HITRAN database ,and an improved detection limit was obtained for interference‐free NH3 monitoring ,this 2.25 μm band has line strengths several times larger than absorption lines in the 1.53 μm band which was often used by NH3 sensors for emission monitoring and analyzing .The measurement system was developed with a new Her‐riott cell and a heated gas cell realizing fast absorption measurements of high resolution ,and combined with direct absorption and wavelenguh modulation based on tunable diode laser absorption spectroscopy at different temperatures .The lorentzian line shape is dominant at ambient temperature and pressure ,and the estimated detectivity is approximately 0.225 × 10-6 (SNR=1) for the directed absorption spectroscopy ,assuming a noise‐equivalent absorbance of 1 × 10-4 .The heated cell experiments with con‐trolled the temperature were performed to validate the sensing strategy .Here the Wavelength Modulation Spectroscopy (WMS) strategy was usually used to measure lower gas concentration for high noise immunity to the non‐absorption transmission losses . The great agreement 2f signal with the calibrated concentration is within the uncertainty at different temperatures by using simple digital signal processing such as multiple averages ,wavelet analysis and so on .The denoise processing has a great advantage in application and implementation over other noise suppression techniques .The result provided a good basis for trace ammonia es‐cape detection based on tunable diode laser absorption spectroscopy .