Impedancemetric gas sensor based on Pt and WO3 co-loaded TiO2 and ZrO2 as total NOx sensing materials

Pt-loaded metal oxides [WO₃/ZrO₂, MO_x/TiO₂ (MO_x = WO₃, MoO₃, V₂O₅), WO₃ and TiO₂] equipped with interdigital Au electrodes have been tested as a NO_x (NO and NO₂) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO₃/TiO₂ showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO₂ in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO_x (NO or NO₂) concentration from 10 to 570 ppm. Pt-WO₃/TiO₂ showed responses to NO and NO₂ of the same algebraic sign and nearly the same magnitude, while Pt/WO₃ and WO₃/TiO₂ showed higher response to NO than NO₂. The impedance at 4 Hz in the presence of NO for Pt-WO₃/TiO₂ was almost equal at any O₂ concentration examined (1–99%), while in the case of Pt/WO₃ and WO₃/TiO₂ the impedance increased with the oxygen concentration. The features of Pt-WO₃/TiO₂ are favorable as a NO_x sensor that can monitor and control the NO_x concentration in automotive exhaust. The effect of WO₃ loading of Pt-WO₃/ZrO₂-based sensor is studied to discuss the role of surface W-OH sites on the NO_x sensing.     

Influence of dioxin reduction on chemical composition of sintering exhaust gas with adding urea

With the addition of urea as an inhibitor, four groups of reducing dioxin emission experiments in sintering pot were conducted. The results show that, adding 0.05%, 0.1% and 0.5% (mass fraction) urea, the emission concentrations of dioxin are 0.287, 0.258 and 0.217 ng-TEQ/m³, respectively. The dioxin emission rates drop substantially compared to 0.777 ng-TEQ/m³ free of urea. With an increase of the urea content, the concentration of SO₂ emission reduces sharply. (NH₄)₂SO₄, formed by the reaction of SO₂ and NH₃, goes into the dust and part of NH3 is released before reaction with the emission of exhaust gas. The NO _x emission presents an increasing trend because the reaction of NH₃ and O₂ at high temperature produces NO _x . Based on the consideration of factors such as the effect of reducing dioxin emission, and the chemical composition of exhaust gas, 0.05% is the optimum adding content of urea.     

操作参数对生物质再燃脱硝特性的影响

以稻壳（RH）、木屑（SD）和生物质炭（BC）3种生物质为对象,利用携带流脱硝试验装置,研究了再燃区反应温度（T2）、再燃区化学计量比（SR2）、停留时间（τ）、NO初始浓度（CNO,in）、水蒸气含量、生物质种类及添加剂等对生物质再燃脱硝效果的影响.结果表明：在T2=850℃-1150℃范围内,随着T2升高,再燃脱硝效率呈现逐渐上升的趋势.在SR2=0.5-1.0范围内,生物质再燃脱硝效率随着SR2降低而逐渐上升.在τ=0.5-1.3 s范围内,生物质再燃脱硝效率随着τ增加呈现先上升后趋于稳定的趋势.在CNO,in=300-600μL/L范围内,生物质再燃脱硝效率随着CNO,in增加逐渐增加,但当CNO,in〉400μL/L时,脱硝效率增加不明显.随着烟气中水蒸气含量增加,生物质再燃脱硝效率呈现先增加后降低并逐渐趋于平稳的趋势,模拟烟气中含有4%水蒸气时的脱硝效率最大.不同生物质的再燃脱硝效率显著不同,RH和SD的脱硝效率明显高于BC.添加剂对脱硝效果有一定的促进作用,其中, NaCl促进作用最为显著.添加剂（Fe2O3）浓度（50-150μmol/mol）对生物质再燃脱硝效率的影响不大.     

Numerical and experimental investigation on emission performance of a fuel staged combustor

The low NOx emission technology has become an important feature of advanced aviation engine.A wide range of applications attempt to take advantage of the fact that staged combustion under lean-premixed-prevaporized(LPP)conditions can significantly cut down emission and improve combustion efficiency.This paper proposes a scheme with fuel centrally staged and multi-point injection.The mixing of fuel and air is improved,and the flame temperature is relative low in combustion zone,minimizing the formation of nitrogen oxides(NOx),especially thermal NOx.In terms of the field distribution of equivalence ratio and temperature obtained from Computational Fluid Dynamics(CFD),a chemical reactor network(CRN),including several different ideal reactor,namely perfectly stirred reactor(PSR)and plug flow reactor(PFR),is constructed to simulate the combustion process and predict pollution emission.The influences of the pilot equivalence ratio and percentage of pilot/main fuel on NOx and carbon monoxide(CO)emission were investigated by CRN model.The effects of the pilot fuel and primary fuel on pollution emission were investigated experimentally.Finally,the effects of pilot equivalence ratio and pilot fuel proportion on NOx emission were discussed in detail by comparing predict of CRN and experimental results.     

330MW燃煤电厂SCR技术的应用研究

研究选择性催化还原法（SCR）在330MW燃煤电厂上的应用,分析了SCR系统工艺流程、工作原理及影响脱硝效率的因素。经过较长时间稳定运行,系统脱硝效率在80%以上,达到设计参数,为燃煤电厂NOx控制提供参考。     

Effect of engine-based thermal aging on surface morphology and performance of Lean NOx Traps

A small single-cylinder diesel engine is used to thermally age model (Pt + Rh/Ba/γ-Al₂O₃) lean NO_x traps (LNTs) under lean/rich cycling at target temperatures of 600 °C, 700 °C, and 800 °C. During an aging cycle, fuel is injected into the exhaust to achieve reproducible exotherms under lean and rich conditions with the average temperature approximating the target temperature. Aging is performed until the cycle-average NO_x conversion measured at 400 °C is approximately constant. Engine-based NO_x conversion decreased by 42% after 60 cycles at 600 °C, 36% after 76 cycles at 700 °C and 57% after 46 cycles at 800 °C. The catalyst samples were removed and characterized by XRD and using a microreactor that allowed controlled measurements of surface area, precious metal size, NO_x storage, and reaction rates. Three aging mechanisms responsible for the deactivation of LNTs have been identified: (i) loss of dispersion of the precious metals, (ii) phase transitions in the washcoat materials, and (iii) loss of surface area of the storage component and support. These three mechanisms are accelerated when the aging temperature exceeds 850 °C—the γ to δ transition temperature of Al₂O₃. Normalization of rates of NO reacted at 400 °C to total surface area demonstrates the biggest impact on performance stems from surface area losses rather than from precious metal sintering.     

氢燃料发动机NOx排放特性与预测

进行了进气管喷射的氢发动机的NOx排放性能的研究,指出了影响氢发动机中NOx排放的因素,并对NOx的排放性能建模.又对降低NOx排放的方法进行了讨论.实验证明点火延迟对降低NOx排放有一定的作用.复合燃烧也可以达到增大输出功率,降低NOx排放的目的.     

煤粉燃烧炉膛沿程NOx释放规律的研究

对一维炉内煤粉燃烧，炉膛沿程NOx的释放规律进行了数值模拟和试验研究。研究结果表明：炉内温度升高，NOx的析出峰值升高，位置前移，温度达到一定值后，随温度的升高, NOx 的释放量又呈下降趋势；煤中含氮量越多，NOx释放量越大，NOx的析出峰值位置，随煤种碳化程度的增加而逐渐后移；随过量空气系数的增加，NOx释放量呈明显增加的趋势；NOx的释放量与煤粉粒度的关系中，存在一个煤粉平均粒度临界值dc，当煤粉粒度d≤dc时，随煤粉粒度的减小，NOx的释放量减小，当煤粉粒度d>dc时，随煤粉粒度的减小，NOx的释放量增大；模拟计算同试验结果吻合较好。     

低NO_x燃烧技术简介

介绍了 NOx的生成途径,根据生成机理的不同介绍了各种低 NOx燃烧技术,包括低氧燃烧、浓淡燃烧、分级燃烧、废气再循环等技术。讨论各种低 NOx燃烧技术在电站锅炉中的应用。同时,介绍了低 NOx燃烧技术在工业锅炉及其它燃烧过程中的应用。     

燃煤锅炉低NOx燃烧技术的研究与应用

结合当前国际上燃煤锅炉低NOx燃烧技术研究的主流方向，介绍了空气分段燃烧和气体再燃技术降低NOx排放的原理。对某电厂300MW机组四角切圆燃煤锅炉进行了空气分段低NOx燃烧系统改造，NOx减排效果达42％；对某电厂50MW燃煤锅炉进行石油气再燃实炉改造示范，NOx减排效果可达61％，证实了这两种技术对降低燃煤锅炉NOx排放的有效性。