DK-9001型氮氧化物分析器

DK-9001型氮氧化物分析器是装在监测车上自动连续测定大气中氮氧化物(NO_x)的环境监测仪器。测量范围0～4毫克/立方米。最小可检量为0.025毫克/立方米。零点漂移24小时不超过4%。用渗透管配制标准气体标定仪器,测量误差不大于5%。反应时间不大于5分钟(达90%值时)。仪器可以监测大气中的氮氧化物(NO_x),或单独测定一氧化氮(NO)或二氧化氮(NO_2)。     

化学发光法氮氧化物分析器的研制

本文介绍了根据一氧化氮和臭氧的气相发光反应原理而研制的氮氧化物分析器。化学发光反应室在正压条件下工作;采用石墨化玻璃炭做为二氧化氮转换成一氧化氮的转换剂。仪器可以分别测量总氮氧化物(NO_x=NO+NO_2)和一氧化氮,测量范围为0—8毫克/立方米,最小可检量为20微克/立方米。     

在线质谱在氢气准确定量中的应用

本研究建立了在线质谱仪准确测定氢气浓度的定量分析方法。通过对内、外管路和真空腔进行清洗,以及增加清洗气通道,优化了在线质谱仪进样清洗方法。通过单通道和多通道切换检测不同浓度的氢气,对仪器的性能进行了考察。优化清洗系统解决了氢气易返回不易抽走的问题,确保了检测结果的准确性。氢气的检出限达到0.001%,在0.005%~5.000%的浓度范围内线性关系良好。该方法可以广泛应用于氢气含量快速、多位点同时监测。     

一种基于LSTM网络的车载NO_x化学传感器温湿度补偿方法研究

氮氧化物是汽车尾气中的重要污染物。采用氮氧化物(NO_x)化学传感器进行污染物检测是监控汽车尾气污染物排放量的一种重要措施,但由于传感器是基于电化学反应的原理,温度和湿度会对化学反应有很大影响,从而导致测量结果不准确。为此,提出一种基于长短期记忆(Long Short-Term Memory, LSTM)网络的车载NO_x化学传感器温湿度补偿方法。LSTM网络利用传感器测量值和真实NO_x浓度值以及测试气体的温度和相对湿度进行训练,从而得到NO_x浓度的测量模型。测试结果表明,该方法具有良好的温度和湿度补偿性能,可以有效提高车载NO_x化学传感器的精度。     

MoS_2/石墨烯复合材料对NO_x气敏特性影响分析

为了快速准确检测汽车尾气中的NO_x气体浓度,采用低温水热法制备了MoS_2/石墨烯复合纳米材料。利用掩膜法将制备的MoS_2/石墨烯镀膜于氧化铝基体表面形成敏感薄膜,制作了一种薄膜型NO_x传感器。采用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HR-TEM)和X-射线光电子能谱(XPS)仪,表征了MoS_2/石墨烯的相组成、微观形貌和电化学特性,分析了MoS_2/石墨烯复合材料对NO_x的气敏机理。在气体传感器静态测试系统上,测试了NO_x传感器灵敏度、温度、响应-恢复、抗干扰和长期稳定等特性。结果表明,MoS_2/石墨烯传感器灵敏度是MoS_2传感器2.1倍,响应时间为3.6 s,恢复时间为9.9 s,具有良好的重复性、选择性和长期稳定性。表明该传感器可实现汽车尾气中NO_x准确检测。     

某2×660MW电厂#2机氮氧化物含量升高的分析

按照目前常规的燃烧方式,在煤炭燃烧过程中产生的氮氧化物NOx主要包括90%的一氧化氮(NO)、5%～10%的二氧化氮(NO2)以及1%左右的N2O等,因此,NOx的生成与排放量主要取决于NO。鉴于此,依据NOx生成原理,结合现场生产实际情况,简要分析了#2机氮氧化物含量升高的原因及控制措施。     

气体中氮氧化物分析方法进展

氮氧化物对环境的危害性比较大,工业生产或者大气环境中对氮氧化物的含量有着严格的控制指标。但不同气体样品中氮氧化物的分析方法由于其含量及基体的不同而不相同。介绍了气体中氮氧化物的仪器直接分析方法包括气相色谱法、化学发光法的特点及适用范围,着重讨论了大气中痕量NO_x的分析方法,主要是现场富集和实验室检测两个方面,比较了各种现场富集方法的工作特点,对这一领域的未来的可能发展方向作了探讨。     

基于光离子化检测器(PID)传感器的便携式毒气检测装置

该装置采用光离子化检测器(PID)传感器进行检测,确保检测的快速性和准确性.装置设有气体选择模式,可准确地检测一氧化氮或硫化氢气体;同时可实现对一氧化氮或硫化氢气体的定量检测.及时、准确、可靠地显示实时的检测有毒气体的浓度,并根据设定的报警浓度提示使用者是否安全.     

基于化学发光检测法的氮氧化物气体分析仪

设计了用于环境空气质量监测系统的、采用化学发光检测法的氮氧化物气体分析仪.氮氧化物的浓度检测利用空气与臭氧发生光化学反应发出荧光,并由新型光电传感器--光电同步式光学平台完成的,该传感器采用相关检测技术实现了低浓度和高浓度氮氧化物气体的高精度检测;根据脉宽调制原理设计了臭氧发生器的高压脉冲电源电路,改用某种活性炭作为NO2转换器的催化荆,增大了气体浓度量程,实现了量程自动切换功能.     

一种应用于煤化工行业过程监测的质谱定量分析方法

为了满足煤化工行业对生产工艺监测与过程控制的需要，建立了一种在线质谱定量分析方法。相比传统在线色谱在煤化工过程监测中的应用，在线质谱监测系统具有实时在线测量组分多、响应速度快、稳定性好、动态范围宽等优点。采用聚光科技Mars-550过程气体质谱分析仪，建立了一种应用于工业过程监控的质谱定量分析方法，包括分析原理、数据采集及处理方法。以合成氨工艺过程控制中气体组分浓度的监测为例，对定量离子的选取、数据处理和结果分析进行了详细的阐述，定量相对误差小于1%。该方法具有实时、快速、准确、多流路、多组分分析的特点。     

Effects of NOX on inhibition of oxidation by ZDTPS

Investigations of the effects of nitrogen oxides (NO_X) on liquid phase oxidation and inhibition have been conducted in order to develop an improved understanding of the processes by which NO_x accelerates oil degradation in internal combustion engines. Results from studies of the effects of NO_x on oxidation of hexadecane (HD) alone, and in combination with a radical trapping (hindered phenol) antioxidant, and preliminary studies with zinc dialkyldithiophosphates (ZDTPs) were presented in previous reports.^1-3 The complexity of reactions involving NO_x and the role in lubricant degradation of NO_x from blowby were described. Those results suggested that NO_x accelerates the rate of consumption of antioxidant additives and, thus, shortens the useful life of the oil. This work describes results of additional investigations with ZDTPs.     

A numerical study on extinction and NOx formation in nonpremixed flames with syngas fuel

The flame structure, extinction, and NO_x emission characteristics of syngas/air nonpremixed flames, have been investigated numerically. The extinction stretch rate increased with the increase in the hydrogen proportion in the syngas and with lower fuel dilution and higher initial temperature. It also increased with pressure, except for the case of highly diluted fuel at high pressure. The maximum temperature and the emission index of nitric oxides (EINO_x) also increased in aforementioned conditions. The EINO_x decreased with stretch rate in general, while the decreasing rate was found to be somewhat different between the cases of N₂ and CO₂ dilutions. The reaction paths of NO_x formation were analyzed and represented as NO reaction path diagram. The increase in N radical resulted in larger NO_x production at high initial temperature and pressure. As the pressure increases, EINO_x increases slower due to the third-body recombination. The thermal NO mechanism is weakened for high dilution cases and non-thermal mechanisms prevail. The combustion conditions achieving higher extinction stretch rate can be lead to more NO_x emission, therefore that the selection of optimum operation range is needed in syngas combustion.     

CFD investigation of NOx reduction with a flue-gas internal recirculation burner in a mid-sized boiler

The demand for reduction of nitrogen oxide (NO_x) emissions from industrial facilities continuously increases, and considerable efforts have been exerted to achieve this goal. In this work, we propose a novel flue-gas internal recirculation (FIR) burner emphasizing the function of FIR to accomplish single-digit NO_x emissions from a mid-/large-sized combustion system. In the new design, a FIR passage is installed inside the conventional non-FIR burner to draw back the flue gas from the combustion chamber and release it into the chamber as a mixture of air and flue gas. The effectiveness of FIR burner is evaluated by employing extensive computational fluid dynamics (CFD) simulations with an enhanced reaction rate model. The existing eddy dissipation model for reaction rate, including the turbulence-chemical interaction, is improved by introducing a position-dependent scaling factor, which is validated by comparison with temperature profiles in experiments. CFD predictions show that a small amount of flue gas returned to the burner still significantly alters the flow structure and temperature distribution. Accordingly, NO_x emission is dramatically diminished (82.83 and 9.7 ppm in the non-FIR and FIR systems, respectively) using the FIR burner. These observations confirm that the new FIR burner effectively accomplishes ultra-low NO_x emissions in field-scale combustion systems. In addition, the fundamentals of NO_x reduction by the FIR burner are thoroughly examined in the present study. The findings will provide essential knowledge in designing other ultra-low NO_x burners.

     

NO2 chemiluminescent emission from flames influenced by acoustic noise

The effect of acoustic noise on combustion is investigated from the perspective of NO_x emissions. A robust, plug-in probe that exploits the natural emission signal from the combustion gases, and which can have practical relevance, is used. Acoustically pulsed flames are stabilized on aburner, and NO₂ chemiluminescence is measured with an intensified detector at various frequencies. The results indicate the NO₂ emission increases in noisy flames at certain frequencies more significantly than others. Noise at higher frequencies in the range 0.8≈1 kHz effects the nitrogen chemistry in stoichiometric flames (ϕ=1), but not that in lean flames (ϕ-0.7 and 0.8).     

Numerical evaluation of NOx mechanisms in methane-air counterflow premixed flames

The control of nitrogen oxides (NO_x) has been a major issue in designing combustion systems, since NO_x play a key role in ozone depletion and the generation of photochemical smog. The characteristics of NO_x emission can be essential information for the development of a clean combustor having suitable reduction methodologies. In the present study, NO_x emission characteristics were evaluated numerically, accounting for the effect of equivalence ratio, stretch rate, pressure, and initial temperature. In general, peak NO_x emission appeared near the equivalence ratio of unity case, and NO_x emission increased with pressure and initial temperature due to the temperature sensitivity in NO_x mechanism. NO_x decreased with stretch rate due to the decrease in residence time in high temperature region. Furthermore, the thermal and prompt mechanisms were evaluated with equivalence ratio for two calculation methods. The conventional methods ignore the interaction of coupled mechanism of thermal and prompt NO_x. The reaction path diagram was introduced to understand effective reaction pathways in various conditions. This paper was recommended for publication in revised form by Associate Editor Kyoung Doug Min Dr. Eun-Seong Cho received his B.S. and M.S. degrees in Mechanical Engineering from Hanyang University, Korea, in 1996 and 1998, respectively. He then received his Ph.D. degree from Seoul National University, Korea, in 2005. He was a principal engineer of KD Navien research center and currently a research associate at Delft University of Technology, The Netherlands. His research interests include eco-friendly clean combustion technology, new and renewable energy systems. Prof. Suk Ho Chung received his B.S. degree from Seoul National University, Korea, in 1976 and Ph.D. degree in Mechanical Engineering from Northwestern University, USA, in 1983. He is a Professor since 1984 in the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests cover combustion fundamentals, pollutant formation, laser diagnostics, and plasma-assisted combustion.     

Effects of NOx on liquid phase oxidation and inhibition at elevated temperatures

Nitrogen oxides (NO_x =NO₂ +NO) play a role in degradation of lubricating oils in internal combustion engines. Interactions of NO_x with fuel derived species have been shown to lead to varnish and deposit formation. Mechanisms of interactions of NO_x with additive and base oil components have not, however, been investigated in detail. The present work describes investigations of the effects of NO₂ on oxidation processes and the fate of NO_x in a model lubricant system. NO₂ acts as a free radical initiator which accelerates the initial rate of uninhibited hydrocarbon oxidation and increases the rate of antioxidant consumption in inhibited systems. NO_x consumption increases after the end of the inhibition period. In addition, NO₂ and NO react with oxidation intermediates or products in a complex series of reactions which can include direct reaction with antioxidants, formation of nitro-oxidation products, conversion of NO₂ to NO and regeneration of NO₂ from NO. The significance of results obtained in this study with respect to mechanisms of oil degradation is discussed.     

Characteristics of NOx emission with flue gas dilution in air and fuel sides

Flue gas recirculation (FGR) is a method widely adopted to control NO_x in combustion system. The recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance a much improved reduction in NO_x per unit mass of recirculated gas, as compared to the conventional FGR in air. In the present study, the effect of FGR/FIR methods on NO_x reduction in turbulent swirl flames by using N₂ and CO₂ as diluent gases to simulate flue gases. Results show that CO₂ dilution is more effective in NO reduction because of large temperature drop due to the larger specific heat of CO₂ compared to N₂ and FIR is more effective to reduce NO emission than FGR when the same recirculation ratio of dilution gas is used.     

A Computer Interfaced,Time-Of-Flight Mass Spectrometer for Studies of Rapid,Gas-Phase Reactions.

ABSTRACT

A gas-phase reactor, consisting of a reaction tube with nine gas reagent injection jets placed axially along its length, has been connected to the ion source of a time-of-flight mass spectrometer. Provision has been made for purifying, and mixing several gases and exciting this mixture by microwave discharge prior to entry into the reaction tube. The mass spectrometer has been interfaced to a dedicated mini-computer system which is capable of simultaneous monitoring of five different masses and on-line control of the setting of one of these mass values. Performance of the system is illustrated by observation of the titration of active nitrogen with nitric oxide.     

A Gas-Mixture Concentration Meter

A concentration meter for multicomponent gas mixtures is described. A layer of doped tin oxide (IV) obtained by the technique of magnetron sputtering of a metal target of complex composition is used as the sensitive element of the primary measuring transducer. The meter allows NH₃ and CO to be analyzed with an error of 1 ppm and is insensitive to NO _x .     

Structure and morphology of Mg–Al–Fe‐mixed oxides derivedfrom layered double hydroxides

The influences of the nature and the extent of M(III) ion substitution on the structure, morphology and surface properties of layered double hydroxides, LDHs [Mg_1?x M(III)_x(OH)₂](CO₃)_x/n·mH₂O, M(III) being Al or/and Fe and x= M(III)/[(Mg+M(III)], and derived mixed oxides were investigated. Three series: Mg?Al, Mg?Al?Fe and Mg?Fe were synthesized using low supersaturation co‐precipitation method at constant pH, with different Mg : Al : Fe ratio and x in the wide range from 0.15 to 0.7 in order to obtain complex, multi‐phase systems with disordered structure, developed surface area, acid–base and redox properties favourable for catalytic application. The morphology of LDHs and their derived mixed oxides did not change considerably although pronounced changes in structural and surface properties occur by thermal decomposition. The increase in Al amount, as well as the deviation of M(III) content from the optimal range for the single LDH phase synthesis, causes the formation of smaller particles and decrease of mixed oxide crystallite size. The nature and amount of M(III) influence the development of surface area, after thermal treatment, depending mainly on the presence of smaller mesopores, not visible by scanning electron microscope. Although the particle size has no considerable influence on the value of the surface area, it was observed that the samples with smaller particles (Mg–Al and Mg–Al–Fe series) have also higher surface area compared with the samples with larger particles (Mg–Fe series).