差分吸收光谱法在线测量排放烟气浓度研究

介绍了差分吸收光谱(DOAS)在线测量系统,分析了DOAS的光谱处理方法.研究了SO2气体浓度的DOAS测量方法,可以实现排放烟气中SO2的在线测量.DOAS法利用数学方法将吸收光谱分解成快变和慢变部分,他利用快变部分计算气体成分的浓度,这使得烟尘干扰和光源强度变化不影响烟气浓度测量精度.DOAS法用线测量代替点测量,可获得区域内更具有代表性的数据,能更准确的反映烟气排放情况;可同时对多种污染物的进行定性、定量分析;是非接触性测量,无需采样.     

基于离散频谱校正的差分吸收光谱数据处理方法研究

差分吸收光谱法(DOAS)常利用傅里叶变换滤波法来滤除光谱数据中的噪声,但因其频率分辨率的限制,致其幅值误差较大,从而影响气体的测量精度.提出了一种离散频谱校正的差分吸收光谱数据处理方法,利用离散频谱主瓣内的谱线重心求出峰值的坐标,对幅值误差进行补偿,提高气体的测量精度.对不同浓度的SO2气体进行了浓度反演实验,结果表...     

废气中粉尘含量的测定方法

将探讨接触式静电法测量烟气流速及烟尘浓度的可行性。采用快速傅里叶变换来计算相关函数计算出速度和流量,实验现象及结果表明,通过浓度实验,建立电压有效值与质量流量的关系。     

紫外烟气连续监测系统在超低排放中的应用

介绍一种基于紫外差分吸收光谱(DOAS)技术,高温全程伴热的超低量程烟气连续监测系统(CEMS-2000L)。其技术指标达到:量程100 mg/m3,线性误差≤±1%FS,24 h零点漂移、量程漂移≤±2%FS,响应时间110 s。将该系统应用于超低排放污染源现场,并且与非分散红外仪表进行比对测试。比对结果显示:测量值与参比方法的绝对误差小于3 mg/m~3,表明高温抽取式紫外DOAS技术适用于固定污染源超低排放的检测需求。     

傅里叶变换轮廓法用于大型三维曲面测量中的数据修正问题

根据傅里叶变换轮廓法的测量原理，提出对大型三维曲面轮廓测量进行光栅频率和横坐标修正的方法和必要性，并进行了实验验证，所得数据的引用误差由修正前的大于０．７％降低到０．３％以内。     

气态元素汞校准的一致性光学评定检测实验研究

利用低压汞灯作为光源,结合单色仪,对汞渗透管法和汞饱和蒸气法气态元素汞校准进行一致性光学评定检测研究。在汞渗透管实验中,吸收度面积值与理论浓度的皮尔逊相关系数为0.996 8,拟合优度为0.993 6,说明两组数据相关性较好且符合郎伯比尔定律。取实验的吸收截面作为标准参考吸收截面,对相同浓度汞蒸气横向对比及不同浓度汞蒸气纵向对比,浓度误差最大为7.45%,表明渗透管法的稳定性较好且精度较高,验证了渗透管法作为汞标气法的可行性。在渗透管实验中加入SO₂,气态汞浓度测量误差最大为12.82%,说明SO₂对汞吸收度测量产生一定程度的干扰。汞饱和蒸气法实验中,以渗透管为基准测得的最大误差在标准允许误差之内,表明2种校准方法具有一致性。但汞饱和蒸气法与渗透管法相比,其重复性及精度仍有不足,待提升空间较大。     

大管径烟道截面积在线测量设备的研制

固定污染源烟气排放连续监测系统(CEMS系统)是环保行业中用来测量烟气排放总量的主要设备,但其计算烟气流量时采用的面积乃是管道的初始面积,和实际情况存在一定的差异,易造成大的测量误差.本文设计了一种大管径烟道截面积在线测量设备,采用激光旋转反射技术,经实验验证,能够有效解决高温高流速烟气条件下烟道截面积的测量问题,提高...     

基于傅里叶红外光谱仪的高温含水烟气中低浓度一氧化氮精确测量研究

随着国家超低排放政策的深入,对烟气中污染物浓度精确测量提出了更高的要求.基于傅里叶红外光谱仪建立了高温含水条件下一氧化氮(NO)气体精确测量系统,在191℃条件下测量了含5％ ～ 20％水蒸气与摩尔分数为5 ～ 40 μmol/mol NO混合前后的吸收光谱,通过修正混合物中H2O的吸光度来精确确定NO浓度,并评价了系...     

烟气排放污染物(SO2)在线监测系统

紫外 可见差分吸收光谱法 (DOAS)是一种可用于在线式烟气排放污染物自动监测的新型方法 ,它在不改变被测试样成分的前提下 ,可以同时对多种气体进行连续测量。对获得的吸收光谱数据由计算机处理 ,可实时记录烟气中各种污染物的含量 ,并对未知成分的气体进行判断。介绍了基于这种测量方法的测试系统的结构、工作原理 ,并利用所建立的测试系统进行了实验研究。测试结果表明 :采用差分吸收光谱法所测得的SO2 浓度在满量程范围内偏差均≤± 1 5 % ,完全可以满足烟气排放污染物 (SO2 )连续在线监测的要求     

基于LabVIEW的多重相关法测量相位差研究

针对全硬件的传统相位测量方法中电路本身的温度漂移、干扰信号及噪声等使测量结果产生误差的问题,结合LabVIEW功能强大、程序开发周期短、图形化编程简单直观以及相关法抗干扰能力强的特点,在虚拟仪器LabVIEW环境下,提出基于快速傅里叶变换(FFT)计算相关函数的多重相关法测量两路信噪比极低的同频正弦波相位差的设计思想和实现方法。通过实测证明:与传统的硬件电路相位差测量方法相比,基于LabVIEW的多重相关法测量相位差具有算法简单、测量精度高、设计灵活等特点,非常适合于微弱正弦信号的参数估计。     

燃煤烟气中Hg迁移转化特性研究

研究了300 MW煤粉锅炉系统选择性催化还原（selective catalytic reduction,SCR）、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施在不同工况、不同煤种情况下的Hg迁移特性和脱除能力。结果表明：各工况下总汞排放浓度为1.16~2.90 μg/m³。最终排入大气中的汞主要以单质汞存在,还有少量氧化态汞,颗粒态汞被全部脱除;汞主要是在海水法烟气脱硫中被去除的,低低温电除尘器、海水脱硫、湿式电除尘器对总汞平均脱除率分别为25%、62%、37%;Hg²⁺占比是影响烟气中汞脱除效率的关键,气相中较高的Hg²⁺份额有利于在电除尘器和海水脱硫装置中获得较高的脱除效率;在该配备SCR脱硝、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施的300 MW煤粉锅炉电厂中,总汞平均脱除率约为83%,能够实现较大程度的汞脱除。     

Interactions between mercury and dry FGD ash in simulated post combustion conditions

Two different flue gas desulfurization (FGD) ash samples were exposed to a simulated flue gas stream containing elemental mercury vapor to evaluate the interactions and determine the effects of gas components, dry FGD ash samples, and temperature on adsorption and heterogeneous oxidation of mercury. Both samples were characterized for surface area, unburned carbon content, element content, and mineralogical composition. Mercury speciation downstream from the sample was determined using Ontario Hydro Method. Results showed that higher levels of mercury oxidation were associated with higher levels of mercury capture. The NO(2), HCl, and Cl(2) promoted mercury oxidation, while SO(2) and NO had inhibitory effects on mercury oxidation. Unburned carbon of dry FGD ash sample played an important role in mercury capture. Whether the surface area was caused by unburned carbon or by calcium-based sorbents might be more significant than the level of surface area. Extent of mercury oxidation and capture increased slightly and then decreased as the temperature rising due to the interaction of mass transfer and reaction rates control.     

燃煤烟气中单质汞的催化氧化技术研究进展

针对燃煤电厂烟气中汞的脱除问题,综述了单质汞氧化催化剂与催化氧化机理的研究现状;着重阐述了碳基、金属及金属氧化物催化剂和选择性催化还原(SCR)催化剂对单质汞的催化氧化性能,分析了活性组分、烟气条件等对各催化剂氧化单质汞性能的影响;指出异相反应是单质汞氧化的重要途径,不同催化剂、不同烟气气氛下氧化机理不同;最后结合我国燃煤电厂的现状,提出深入研究单质汞的催化氧化机理,进一步提高SCR催化剂的催化氧化单质汞活性、抗硫性及稳定性将是燃煤烟气汞污染控制技术的重点发展方向。     

基于卡尔曼滤波理论的气体浓度反演算法

广泛应用于气体探测的差分吸收光谱技术(DOAS)利用气体分子的窄带吸收特性结合最小二乘算法来推演气体浓度.但是,最小二乘法在外界环境因素干扰的情况下,往往产生较大的误差.本文引入了基于状态空间理论的气体浓度定量分析算法.通过把浓度变化视为状态方程,把光强吸收变化看作测量方程,从而组成状态空间方程,然后将卡尔曼滤波应用到气体状态空间中实现浓度反演.对于噪声统计信息未知的情况,通过自适应滤波算法,在滤波过程中利用已有的历史信息对噪声实现估计,从而使得整个系统在信噪比较低的情况下也能取得较好的反演精度.最后通过实验对最小二乘算法和卡尔曼滤波算法进行对比,证明卡尔曼滤波算法更具优越性.     

Acousto-optic differential optical absorption spectroscopy for atmospheric measurement of nitrogen dioxide in Hong Kong

Measurement of the atmospheric concentration of nitrogen dioxide (NO(2)) pollutant was demonstrated by differential optical absorption spectroscopy (DOAS) using a visible acousto-optic tunable filter. In a traditional spectral scanning DOAS system for atmospheric concentration monitoring, a highly stable light source is required. When the light intensity fluctuates during scanning, the concentration retrieval will be inaccurate. In order to reduce the error due to intensity fluctuations, a modified DOAS system has been developed by introducing a broadband light intensity monitoring channel. Using the measured intensity of the broadband channel as the intensity of the light source, the spectrum can be de-biased and the residual intensity variation will primarily result from atmospheric extinction. In addition, by employing the lock-in detection technique, the background light interference is also removed in the modified DOAS system. The atmospheric NO(2) concentration measurement was performed at the campus of City University of Hong Kong, and the results were compared with the concentration reported from a nearby monitoring station in Sham Shui Po, operated by the Hong Kong Environmental Protection Department.     

Numerical simulation on adsorbent injection system for mercury removal from coal-fired flue gas

Optimizing the injection system significantly reduces the cost of adsorbent injection technology for mercury removal from coal-fired flue gas. In this work, the effects of three common injection system layouts, namely single-sided four-way pipe (SFP), quadtree (QT), and long to short (L-S), on adsorbent particle concentration, mercury concentration, and mercury removal efficiency were systematically investigated by simulation calculation. It shows adsorbent coverage, and particle concentration standard deviation coefficient at the initial injection satisfies SFP > QT > L-S. The number of nozzle and injection directions affect the distribution of adsorbent particle concentration. The apparent mercury removal occurs within 2 s after adsorbent injection. The SFP arrangement has the best average coverage rate of adsorbent (86.86%), average standard deviation coefficient (2.40), and mercury removal efficiency (60.12%). The coupling degree between particle concentration and flue gas mercury concentration field is essential in determining mercury removal performance.     

Application of genetic algorithm-back propagation for prediction of mercury speciation in combustion flue gas

Coal combustion is one of the main sources of mercury emission. Studies using artificial neural networks (ANNs) to predict mercury emission have shown the feasibility of ANN method. Such analyses aimed to provide guidance for mercury emission control in coal combustion. A mercury emission prediction model was developed by modifying the traditional back propagation (BP) neural networks, and a genetic algorithm (GA) based on global search was used, so called the GA-BP neural networks. In total, six main factors were evaluated and selected as the characteristics parameters. Totally, 20 coal-fired boilers were used as training samples, and three different types of mercury including elemental mercury, oxidized mercury, and particulate mercury were used as outputs. The accuracy of prediction results was analyzed, and source of error was discussed. Results show that correlation efficiency for the training samples was as high as 0.895. Three additional samples were studied to test the predictive model. Results of training and predicting were highly correlated with actual measurement results. It is shown that GA-BP is a promising model for mercury speciation prediction.     

烟气在线监测系统及思考

固定污染源排放的烟气会对环境造成污染,对其进行科学监测至关重要。本文介绍了现有的烟气在线监测系统,包括空气质量自动监测系统、烟气排放连续监测系统、差分光学吸收光谱法在线连续监测系统、物联网下无线传感器网络技术在线监测系统等,介绍了每个系统的组成、技术特点、监测方法、实际应用和发展方向,并从量值溯源和远程校准两个方面对烟气在线监测系统与计量系统的关系进行了阐述。