车用柴油机排放NOx催化还原净化初探

简要分析柴油机NOx的产生机理、控制方法；比较各种柴油机NOx催化还原净化技术的特点；根据车用柴油机工作要求，确定了适合车用柴油机NOx净化的NH3—SCR方法，进行发动机台架实验，分析了实验结果。     

Catalytic Effects of Minerals on NOx Emission from Coal Combustion

Abstract

The catalytic effects of inherent mineral matters on NO _x emissions from coal combustion have been investigated by a thermo-gravimetric analyzer (TGA) equipped with a gas analyzer. The effect of demineralization and the individual effect of Na, K, Ca, Mg, and Fe on the formation of NO _x are studied as well as the combined catalytic effects of Ca + Na and Ca + Ti. Demineralization causes more Fuel-N to retain in the char, and reduction of NO _x mostly. But the mechanistic effect on NO _x formation varies from coal to coal. Ca and Mg promote NO _x emission. Na, K, Fe suppress NO _x formation to different extents. The effect of transition element Fe is the most obvious. The combination of Ca + Na and Ca + Ti can realize the simultaneous control of sulfur dioxide and nitrogen oxides emissions.     

NOx control by air staging in a small biomass fuelled underfeed stoker

There is a need to develop improved designs of environmentally acceptable thermal plant for use in process industries in developing countries. Such plant may take advantage of the underfeed combustion principle which exhibits a tolerance towards smoke emission in the burning of high volatile matter biomass fuels. This paper describes an experimental investigation into the conversion of a small, 30 kW underfeed stoker from coal to wood chip firing. Two methods of air staging are considered for NO_x abatement, including a novel air deflection technique. Comparisons are made between plant performances using the two methods. The results are also compared against representative values for coal firing. It was concluded that the air deflection technique showed potential as a means of NO_x minimisation in small, underfeed stokers taking into account other requirements of adequate plant thermal efficiency and exhaust gas combustion quality. Copyright © 2000 John Wiley & Sons, Ltd.     

电站锅炉NOx排放控制的技术经济分析

根据近年来NOx排放控制技术的发展情况，总结了各种低NOx控制技术的特性以及其工程应用的技术经济性，可为电站锅炉的NOx排放控制技术改造提供参考，最后提出了低NOx技术可能的发展方向。     

乙醇选择催化还原降低柴油机NOx排放的应用研究

以Ag/Al2O3作为催化剂、乙醇为还原剂的选择性催化还原(SCR)技术被认为是最有潜力降低稀燃NOx的技术之一。开发了基于开环控制的还原剂空气辅助喷射系统;在发动机台架上对乙醇选择性催化还原Ag/Al2O3催化剂的特性进行了性能评价试验;对与Ag/Al2O3组合使用的Cu/TiO2和Pt/TiO2氧化催化剂进行了匹配优选;对集成NOx排气后处理的整机进行了ESC工况测试试验;最后将集成的排气后处理系统装在一辆客车上,并进行了道路实车试验。台架试验结果表明:新鲜Ag/Al2O3催化剂具有很高的NOx转化效率,老化一段时间后NOx转化效率有所降低;与Ag/Al2O3 Cu/TiO2组合催化剂相比,Ag/Al2O3 Cu/TiO2 Pt/TiO2组合催化剂具有更好的NOx转化效率,并能抑制THC和CO排放升高;使用NOx集成排气后处理系统后,发动机在欧ⅢESC工况下,NOx从原机的13.06 g/(kW.h)降为4.63 g/(kW.h),整机的NOx、THC、CO排放都低于欧Ⅲ限值。道路实车试验表明,Ag/Al2O3催化剂需要进一步降低催化剂的起燃温度,以适应柴油车实际运行中低温变工况的需要。     

煤与生物质混烧时NO_x排放特性的实验研究

叙述了将稻壳、麦秆、松木屑3种生物质,分别与阳泉煤掺烧时,不同掺混比与过量空气系数对NOx排放规律的影响。指出,在低含O2量区,无论单煤还是混合燃料,NOx浓度均随烟气中的含O2量增加而增大;不同燃料NOx浓度增长速度的快慢,随烟气中的含O2量增加有所不同;在高含O2量区,混合燃料NOx的排放量随烟气中含O2量的增加而降低;生物质与煤掺混对NOx排放规律的影响不明显,燃烧过程中NOx的排放受生物质本身的含N量、煤种以及燃烧方式的影响较大。     

某200 MW四角切圆锅炉燃烧器改造降低NOx数值模拟

针对国内某电厂200MW四角切圆锅炉NOx排放量较高,结渣严重的问题,利用CFD软件平台,采用数值模拟方法对其改造前后炉内燃烧过程进行研究。计算结果表明:由于附壁射流的作用,使得高温区集中在炉膛中部,有效地防止了锅炉结渣;改造后炉内有比常规燃烧方式锅炉更大的还原气氛区域,抑制了NOx的产生,使其排放降低34.6%。改造后的计算结果与试验相符的较好,所以此次数值模拟为锅炉设计、改造和运行提供理论依据。     

燃煤电站锅炉NOx排放的控制措施

基于我国燃煤电站锅炉NOx排放的实际情况,在对影响其NOx排放各因素进行分析的基础上,细化了低氧燃烧、空气分级燃烧、低NOx燃烧器和燃料分级燃烧技术在我国电站锅炉的应用,指出锅炉设计中应尽可能选用切向燃烧方式,将再燃技术应用于降低燃用低挥发分煤的固态排渣电站锅炉设计和改造中以进一步降低NOx排放并满足国家标准的要求,锅炉运行中尽量减小各喷口风粉量的偏差,合理组织沿炉膛水平方向和高度方向(倒梯形、缩腰形等)的分级燃烧实现降低NOx排放的最佳效果.     

利用SCR技术降低柴油机NOx的试验研究

设计了尿素水溶液还原添加装置,并使用这套装置在发动机台架上进行了稀燃NOx选择催化还原（SCR）催化剂的性能评价试验,最后分析了SCR技术目前存在的问题。试验结果表明：在30000h^-1空速、排气温度为340～420℃范围的条件下,该催化剂的NOx转化率维持在90%以上,而在低温和高温下的转化率较低;随着尿素水溶液添加量的增加,催化剂NOx转化率提高,但同时会增加CO排放;当空速为50000h^-1时,催化剂性能略有所下降。     

微型燃气轮机燃烧室NOx排放性能实验研究

作为微型燃气轮机的核心部件之一,燃烧室性能的优劣将直接影响微型燃气轮机的整体性能。随着环保意识的增强和环保法规的日益严格,控制燃烧室污染物的排放业已成为一个重要课题。以一微型燃气轮机燃烧室为对象进行了热态条件下NOx排放性能的实验研究。实验结果表明：随着过量空气系数的增加,NOx的排放浓度呈下降趋势;燃烧区温度的升高以及在高温区停留时间变长,NOx生成量大大上升;在较高负荷工况下,NOx的排放量较小。     

含Pd双金属分子筛催化剂控制稀燃汽油机NOx排放

为实现对稀燃汽油机NOx排放的有效控制，对Pd-In-ZSM5、Cu-Pd-ZSM5催化剂在实际稀燃排气条件下进行了研究，对Pd-In-ZSM5催化剂，由于Pd、In两种金属的作用，出现了两个NOx转化效率的峰值，最高转化效率达到35．7％．Cu-Pd-ZSM5催化剂可以实现CO对NOx的还原反应，使稀燃NOx的转化效率最高达到60％，并且具有较宽的活性温度窗口；当量空燃比时，NOx的转化效率超过70％，含Pd的双金属分子筛催化剂，在不同的温度范围内，可以实现HC和CO对NOx的协同还原反应，有效拓宽较高NOx转化效率的活性温度窗口。     

Effect of hydrogen on compression-ignition (CI) engine fueled with vegetable oil/biodiesel from various feedstocks: A review

Compression ignition (CI) engines used in the transportation sector operates on fossil diesel and is one of the biggest causes of air pollution. Numerous studies were carried out over last two decades to substitute the fossil diesel with biofuels so that the net carbon dioxide (CO₂) emission can be minimized. However, the engine performance with these fuel was sub-standard and there were many long-term issues. Therefore, many researchers inducted hydrogen along with the biofuels. The present study gives an outlook on the effect of hydrogen addition with biodiesel/vegetable oil from various sources in CI engine. Engine parameters (brake thermal efficiency, brake specific fuel consumption), combustion parameters (in-cylinder pressure and heat release rate) and emission parameters (unburned hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and smoke emissions) were evaluated in detail. The results show that hydrogen induction in general improves the engine performance as compared to biodiesel/vegetable oil but it is similar/lower than diesel. Except NOx emissions all other emissions showed a decreasing trend with hydrogen addition. To counter this effect numerous after-treatment systems like selective catalytic reduction (SCR), exhaust gas recirculation (EGR), selective non-catalytic reduction system (SNCR) and non-selective catalytic reduction system (NSCR) were proposed by researchers which were also studied in this review.     

600MW燃煤机组NOx排放的试验研究

在分析NOx生成机理的基础上,用试验的方法研究了过量空气系数、燃烧器倾角以及顶部燃尽风开度对NOx排放浓度的影响。研究结果表明：在相同负荷下,过量空气系数从1．14（氧量为2．5％）至1．27（氧量为4．5％）的过程中,NOx排放浓度随之增加且;燃烧器摆角自下向上摆动时,NOx排放浓度不断减小;顶部燃尽风开度增大时,NOx排放量降低。     

Hydrogen effects on NOx emissions and brake thermal efficiency in a diesel engine under low-temperature and heavy-EGR conditions

Cooled and heavy exhaust gas recirculation (EGR) has been used to control NOx emissions from diesel engines, but its application has been limited by low thermal efficiency or high unburned hydrocarbon emissions. In this study, hydrogen was added into the intake manifold of a diesel engine to investigate its effect on NOx emissions and thermal efficiency under low-temperature and heavy-EGR conditions. The energy content of the introduced hydrogen was varied from an equivalent of 2-10% of the total fuel’s lower heating value. A test engine was operated at a constant diesel fuel injection rate and engine speed to maintain the same engine control unit (ECU) parameters, such as injection time, while observing changes in the carbon dioxide produced due to variations in the hydrogen supply. Additionally, the EGR system was modified to control the EGR ratio. The temperature of the intake gas manifold was controlled by both the EGR cooler and the inter-cooling devices to maintain a temperature of 25 °C. Exhaust NOx emissions were measured for different hydrogen flow rates at a constant EGR ratio. The test results demonstrated that the supplied hydrogen reduced the specific NOx emissions at a given EGR ratio while increasing the brake thermal efficiency. This behavior was observed over constant EGR ratios of 2, 16, and 31%. The rate of NOx reduction due to hydrogen addition increased at higher EGR ratios compared with pure diesel combustion at the same EGR ratio. At an EGR ratio of 31%, when the hydrogen equivalent to 10% of the total fuel’s lower heating value was supplied, the specific NOx was lowered by 25%, and there was a slight increase in the brake thermal efficiency. This behavior was investigated by measuring and analyzing changes in the exhaust gas composition, including oxygen, carbon dioxide, and water vapor.     

Estimation of NOx and soot emission from a constant volume n-butanol/n-dodecane blended spray using unsteady flamelet model based on n-dodecane/n-butanol/NOx/PAH chemistry

A 246 species and 1062 reactions containing skeletal n-dodecane/n-butanol/NOx/Polycyclic Aromatic Hydrocarbon (PAH) combustion mechanism (Mix246) was developed for n-dodecane/n-butanol blend combustion under diesel engine-like conditions. The Mix246 mechanism was validated using ignition delay and species concentration profile data from various n-dodecane and n-butanol combustion experiments as well as by comparisons with predictions from the parent mechanisms. Subsequently, the Mix246 mechanism was coupled with a 3D Computational Fluid Dynamic (CFD) solver to simulate turbulent combustion of n-butanol/n-dodecane blended sprays in a constant volume combustor using an unsteady flamelet model. The CFD model for the 100% n-dodecane case was benchmarked against the non-reacting and reacting Spray-A conditions of the Engine Combustion Network (ECN). Finally, a parametric study was conducted to investigate the effects of various diesel engine-like conditions such as fuel injection pressure, initial ambient pressure and temperature conditions and varying n-butanol/n-dodecane blend ratios on NOx and soot emissions. Simulations show that the turbulent spray combustion evolves through distinct temporal stages and that the fully developed flame have spatially separated zones of reactive physics. Combustion properties and emission profiles for pure n-dodecane and blends with up to 20% n-butanol were seen to be nearly identical suggesting that n-butanol is a suitable alternative biofuel for CI engine combustion.     

燃煤过程中NOx的生成机理及控制技术

简述了煤燃烧过程中NOx的生成途径、生成机理以及排放的影响因素。通过分析燃煤过程中NOx的生成过程,阐述了控制其生成和降低排放的原则,并且探讨了目前较常用的几种控制NOx污染的技术措施和存在的问题,指出了脱氮技术的现状及发展方向。     

分级燃烧降低燃煤锅炉NOx排放的机理及影响因素分析

再燃燃料在还原性气氛下对主燃区煤粉燃烧生成的氮氧化物的还原反应中 ,再燃燃料中产生的中间产物氰基、氨基和烃根等起到分解氮氧化物的作用。同一再燃燃料中烃类物质在富燃料和贫燃料气氛中所起作用截然不同。实际应用中应使再燃区内各处处于弱还原性气氛下以保证再燃降低NOx 排放的效果 ,并尽量采用气体燃料作为再燃燃料 ,同时在获取所需NOx 排放水平前提下尽量选取较高的空气过量系数(化学当量比 ) ,以同时降低飞灰中的含碳量、减轻高温腐蚀的程度。     

车用催化转化器流场的数值模拟

本文用当量连续法建立了蜂窝载体的流体力学模型 ,并用CFD软件对整个催化器的流场进行了稳态流动数值模拟。模拟结果显示 :气流在圆锥管壁面附近出现了分离并产生较强的扰动 ,造成气流局部压力损失和载体前气流速度分布不均匀 ;此外 ,扩张角越大 ,催化器流速分布不均匀性和压力损失越大 ,但当扩张角增大到一定程度后 ,扩张角对流速分布和压力损失的影响变小。     

车用催化器非稳态性能的数值模拟

采用数值模拟的方法考察了车用催化器的非稳态性能。模拟结果正确地反映了冷启动过程中催化器载体温度场的变化规律，并且表明了气体浓度场的变化规律。     

基于线性神经网络与柴油十六烷值预测发动机NOx排放

分别以柴油的十六烷值、十六烷值和十六烷改进剂、十六烷值和柴油的含氮量作为输入量,以发动机排放的NOx作为输出量,建立了发动机的NOx排放的线性神经网络模型,利用该模型预测了发动机排放的NOx的值,分析了十六烷改进剂和柴油的含氮量对发动机的NOx排放的影响,得到了较为满意的结果。