CH4/空气混合物中含N、S组分对生成污染物的影响

本文采用详细的CH4/空气反应机理,在良搅拌反应器的条件下,计算了初始含NH3、HCN和H2S对污染物NO和SOx(SO、SO2)生成规律的影响.结果表明,初始含N、S的组分可使NO和SOx的排放量明显增加.同时还利用敏感性分析对污染物形成的重要反应进行讨论.     

原位漫反射红外光谱研究NO在Ag/SAPO-34催化剂上的选择性催化还原

原位漫反射红外光谱研究NO在Ag/SAPO 34催化剂上的选择性催化还原过程。考察了以丙烯为还原剂 ,在富氧及 573～ 773K温度条件下的反应。通过比较初始混合气中加氧或不加氧时反应的原位光谱 ,探讨了氧在NO还原过程中的作用。结果表明 ,氧能充分促进丙稀活化以及增加NOx 吸附态含量 ,并且氧的存在是有效产生有机 氮氧化物 (R NO2 ,R ONO)不可缺少的条件。基于光谱实验 ,认为反应机理为 :NO ,丙烯和氧反应 ,在Ag/SAPO 34催化剂上生成吸附的有机 氮氧化物 ,再由这些吸附物种分解成N2 ,催化还原的关键是形成有机 氮氧化物中间体。     

加压富氧燃烧下SO_3生成特性的动力学机理研究

加压富氧燃烧技术由于受燃烧压力和烟气再循环富集SO_2的影响,烟气中SO_3的形成存在加剧的风险。本文通过详细化学反应机理和热力学平衡计算,对0.1~2.5 MPa范围内加压富氧燃烧条件下一些关键因素对SO_3形成的影响进行分析。研究结果表明;加压燃烧显著缩短2SO_2+O_2→2SO_3总包反应体系达到平衡的时间,并促进了SO_3的生成量,压力从0.1 MPa.提高到1.5MPa,对应的SO_3浓度升高到4倍,酸露点温度升高71℃。在高温火焰区(T≥1473K),0.1~2.5 MPa压力范围下,反应体系的平衡时间在1~100 mS的量级,SO_3的生成率在0~6.5%;而在后火焰区(T≤1273 K),反应速率较慢,反应体系的平衡时间在1~1000 s的数量级。通过对火焰区SO_3生成特性的热力学平衡评估发现SO_3的生成量分别与SO_2和O_2的浓度呈1和0.5次方的关系。     

采用详细化学反应机理研究煤富氧燃烧NO_x生成机制

本文采用详细化学反应机理,建立氧煤燃烧气固反应模型,分析煤在富氧燃烧条件下NO_x生成机制,研究不同O₂浓度和分级燃烧对NO_x排放的影响。富氧燃烧时,NO_x生成主要路径为:HCN→CN→NCO→NO和HCN→CN→NCO→HNCO→HN₂→NH→HNO→NO。初始O₂增大,挥发分和HCN析出时间提前,高的O₂初始浓度对燃料N转化率有促进作用;煤富氧分级燃烧时,主燃区还原气氛有利于NO还原为N₂,其主要还原路径如下:NO+CO→N+CO₂、NO+H→N+OH和NO+N→N₂+O,当主燃区过量空气系数SR₁从1.15减小到0.6,N最终转化率（t=1000 ms）只是从0.379减小到0.339,相对于未分级燃烧时变化了10.55%,与煤空气分级燃烧相比,煤富氧分级燃烧对N转化率影响较小。     

富氧燃烧详细机理评估及机理简化

在富氧燃烧中,反应物被大量CO_2稀释,其反应动力学发生明显变化。本文系统地研究了甲烷富氧燃烧的详细机理和骨架机理.为此,首先对6个详细机理在典型富氧燃烧实验下的氧化性能进行评估.然后将预测精度最好的详细机理与不同NO_x机理进行耦合与验证,找出对NO预测最好的机理。最后将预测氧化和NO都最好的详细机理进行了机理简化,并进行了系统验证。结果表明,USC-MechⅡ机理在富氧燃烧工况下具有最好的氧化预测精度,且有效考虑了富氧燃烧下CO_2化学影响引起的CO浓度变化;USC-MechⅡ机理耦合GRI-Mech 2.11中NO_x机理对NO排放预测精度最好;本文简化得到的38组分、180步反应的骨架机理在点火延迟时间、火焰传播速度以及PSR中温度和NO排放预测等方面和详细机理具有很好的一致性。     

富氧燃烧烟气压缩脱硫脱硝的实验研究

富氧燃烧技术是实现CO_2捕获的重要方式,研究表明其特有的烟气压缩纯化过程可实现NO_x、SO_2的协同脱除。本文在可在线监测的加压实验台架上开展实验,探讨了干态和湿态条件下影响NO_x、SO_2脱除的因素及二者间相互影响关系。结果表明,加压有助于NO转化为NO_2,干态下高浓度SO_2会抑制此过程。湿态下加压会促进NO_x和SO_2转变为硝酸和硫酸,NO_x的脱除率与系统压力和初始NO浓度成正比,SO_2的存在一定程度上会抑制NO_x的脱除,但NO的存在则对SO_2的脱除有益。     

利用链式反应同步氧化烟气中NO和SO2的研究

燃煤烟气中NO和SO2的氧化对于提高其脱除效率和改良脱除产物有重要意义。基于大气化学的研究成果,本文提出了利用链式反应同步氧化烟气中NO和SO2的设想。阐述了该方法的反应机理,数值实验研究了在烟气条件下该链式反应发生的可能性以及反应温度对NO和SO2氧化率的影响,提出了利用低成本的添加剂引发链式反应的方法,并分析了选择添加剂的原则。     

高浓度CO2气氛下燃煤氮、硫污染物的释放特性

采用污染物在线分析仪、气相便携红外分析仪研究了程序升温条件下改变氧化介质时煤中氮,硫的释放特性以及含硫物相的浓度变化规律,探讨了不同气氛,CO2浓度与O2浓度单独变化时对NO、SO2析出特性的影响机理.结果表明:O2/CO2燃烧气氛下NO、SO2排放峰值及总量均低于O2/N2气氛.CO2气氛下烟气中存在大量的CO,有利于NO的降解,同时也促进了烟气中其他含硫物相的形成,随着CO2浓度的增加,特别是在燃烧后期,NO、SO2的排放显著降低.O2浓度改变对NO和SO2的释放影响不同:O2浓度升高促进了SO2的析出;但是O2浓度在一定范围内增加对NO的排放并无明显影响,随着O2浓度进一步增加,NO的释放峰向低温区迁移,同时排放量降低.     

富氧燃烧条件下煤焦的燃尽特性

本文利用平面火焰携带流反应器研究了DT烟煤在富氧燃烧条件下的燃烧实验。采用灰示踪法分析煤焦的燃尽和元素释放特性,并采用等密度模型计算了基于氧化反应C+0.5O_2→CO的表观反应动力学参数。研究结果表明;煤粉在富氧燃烧条件下的燃尽慢于空气燃烧;富氧燃烧条件下,煤焦与CO_2的气化反应会导致煤焦表面对O的化学吸附,进而导致氧元素释放速率减慢;高氧浓度条件下,高浓度CO_2对煤焦燃尽的抑制作用大于CO_2气化反应对煤焦燃尽的促进作用,降低环境氧浓度可以逐步提高CO_2气化反应对煤焦燃尽的贡献。     

红外光谱研究大气痕量气体在α-Al_2O_3表面上的协同反应

利用傅里叶变换显微红外光谱仪(micro-FTIR)研究SO2/O3,SO2/NO2在α-Al2O3颗粒物上的协同反应。结果表明,O3和NO2都可以氧化SO2在α-Al2O3矿尘上反应形成硫酸盐。比较生成的硫酸盐峰面积随反应时间的变化可以发现,O3/SO2在颗粒物表面的反应速率较NO2/SO2快。     

北京限行期间大气污染物的DOAS监测与分析

摘要：利用差分光学吸收光谱（DOAS）技术于2007年8月对北京市朝阳区大气污染物进行了实时监测,对大气中重要常规污染物NO2、SO2和O3的日变化特征、与天气条件之间的关系和各污染源进行了分析和探讨。通过分析污染物在“好运北京”奥运限车期间（8月17～20日 ）与限车前后（8月16、21日）的浓度变化,对机动车限行效果进行了讨论。结果表明,监测点NO2主要来源于汽车尾气,以凌晨和上午时段污染最重,并对O3的来源有着一定的贡献;SO2主要来源于西南方向的污染源,较强风速时北风有利于其浓度的降低;结果还显示机动车限行可有效降低NO2 、SO2浓度,分别达到28.34％和25.87％;但是因导致O3被消耗量降低,致使O3浓度上升。     

NH3NO interaction at low-temperatures: An experimental and modeling study

The present work provides new insight into NH₃NO interaction under low-temperature conditions. The oxidation process of neat NH₃ and NH₃ doped with NO (450, 800 ppm) was experimentally investigated in a Jet Stirred Flow Reactor at atmospheric pressure for the temperature range 900–1350 K. Results showed NO concentration is entirely controlled by DeNO_x reactions in the temperature range 1100–1250 K, while NH₃NO interaction does not develop through a sensitizing NO effect, for these operating conditions.A detailed kinetic model was developed by systematically updating rate constants of controlling reactions and declaring new reactions for N₂H₂ isomers (cis and trans). The proposed mechanism well captures target species as NO and H₂ profiles. For NH₃NO mixtures, NO profiles were properly reproduced through updated DeNO_x chemistry, while NH₂ recombination reactions were found to be essential for predicting the formation of H₂. The role of ammonia as a third-body species is implemented in the updated mechanism, with remarkable effects on species predictions. For neat NH₃ mixture, the reaction H+O₂(+M)=HO₂(+M) was crucial to predict NO formation via the reaction NH₂+HO₂H₂NO+OH.     

碳氢扩散火焰实验研究：燃烧气氛对火焰光谱与温度的影响

辐射是各种燃烧过程中热传递的主要方式。在不同的火焰中,辐射光谱分布十分复杂。在这项工作中,利用光谱仪测量了可见光(200～900 nm),近红外(900～1 700 nm)和中红外(2 500～5 000 nm)波段火焰的光谱强度,分析了空气和富氧气氛下扩散火焰的光谱特征。并基于光谱分析,定量得到了火焰中碳烟以及气体发射的辐射力,计算了火焰的温度分布。结果表明,空气燃烧中的火焰温度低于富氧燃烧中的火焰温度。在空气气氛下,火焰中的碳烟和气体均对中的热辐射起着重要作用。而在富氧气氛下,气体对于火焰热辐射更为重要。在可见光和近红外波段,由于在空气气氛下火焰中碳烟的大量形成,光谱曲线显示出了良好连续性。而富氧气氛下火焰的辐射光谱降低。在中红外波段,空气气氛下火焰的气体辐射明显弱于富氧气氛下火焰的气体辐射。     

Sonochemical formation of nitrate and nitrite in water

The formation of nitrite and nitrate ions in water under irradiation with 900 kHz ultrasound was studied as a function of time, temperature and gas (oxygen/nitrogen) composition. The rate decreases as temperature increases, and is below the detection limit when there is no O2 gas present. The absolute rate of formation of NOx- ions obtained (about 30 x 10(-9) mol min-1 W-1) agrees well with previous similar studies. The differences in the NO2-/NO3- ratio found between various studies can be satisfactorily explained though a mechanism where HNO2 and HNO3 are formed in the gas phase of the imploding cavity, and then dissolve in the water and dissociate to ions. The NO2- species is initially substantially favoured, as considerably more NO is formed than NO2. Thermodynamic calculations indicate that at the 'hot spot' temperature of about 5000 K believed to be present, there would very large amounts of NO and OH radicals present, and at such high temperatures, thermodynamics would be a good approximation of the situation, since the rates of reactions would be very rapid. The reaction needs O2 in order to proceed to a significant degree; no NOx- was detected in the absence of oxygen gas.     

傅里叶红外光谱法研究AP的快速热分解

用T-Jump/FTIR联用技术研究了模拟燃烧条件下AP的快速热裂解。在不同压力的高纯氮气条件下,以1000K.s-1的升温速率达到设定的温度(874和1274K)快速分解,用快速扫描傅里叶变换红外光谱原位实时分析分解产物的种类和浓度变化。结果表明,AP热裂解主要气相产物为NO2,N2O,NO,HCl和NOCl等,实验温度和压力都使AP快速热裂解气相产物N2O/NO2,NO/NO2和NO/NOCl的比值提高,因此认为AP不但存在凝聚相和非均相的气相/凝聚相反应,而且还有主要气相产物之间的"后续反应"。     

不同因素影响下Fe(Ⅲ)水解中和法制备FeOOH矿相的光谱分析

羟基氧化铁(FeOOH)作为重金属等污染物的吸附材料倍受关注,但不同因素作用下形成的FeOOH产物矿相、结构性质的差异及其对环境功能的影响,却少有报道。采用X射线衍射仪,红外光谱仪,扫描电子显微镜和激光粒度分析仪,系统考察了Fe(Ⅲ)溶液水解中和形成FeOOH时,不同作用因素如铁盐种类、pH和温度等对产物矿相的影响。结果表明,pH 8条件下,Fe(Ⅲ)溶液水解产物均为二线水铁矿(Fe₅HO₈·4H₂O);随着pH升高,Fe₅HO₈·4H₂O会向α-FeOOH相转化。Cl-和NO-₃离子的存在分别有利于β-FeOOH和α-FeOOH的形成;SO2-₄会阻碍Fe₅HO₈·4H₂O向α-FeOOH相转化;Fe2+存在时,会促进Fe₅HO₈·4H₂O向α-FeOOH相转化。加热陈化,可促进Fe₅HO₈·4H₂O转化为α-FeOOH,且利于良好结晶α-FeOOH的形成。但pH≤5,富含Cl-的Fe(Ⅲ)溶液加热水解利于β-FeOOH的生成。不同因素影响下形成的FeOOH,在矿相、表面基团、颗粒形貌和粒径大小上存在一定的差异。     

Computation of NO x emission of a methane - air diffusion flame in a two-dimensional laminar jet with detailed chemistry

NOx formation from a methane - air diffusion flame in a two-dimensional jet involving highly preheated air, which has recently become an important topic in industrial furnaces, is investigated numerically using a full chemistry approach including C2, prompt and thermal mechanisms. Effects of increased air temperature on NOx formation are examined. Numerical results show that both NO formation mechanisms increase dramatically with increasing air temperature. A C-shaped production zone of NOx, corresponding to the fuel-lean and fuel-rich regions of triple flame, is identified. It is shown that NO formation with high air temperature can be suppressed efficiently by decreasing the oxygen concentration in the airstream. Production rate analyses of elementary reactions are made. Formation paths of NOx at low and high temperatures are obtained and compared. The results show that the NOx formation path depends strongly on the air temperature. In addition to the thermal route and the HCNNO route, the HCNCN and NOCN recycling routes are greatly enhanced at high air temperature. The results show that the prompt mechanism and the thermal mechanism are strongly coupled at high air temperature. Calculations of prompt NO and thermal NO in a two-dimensional jet and in the counterflow configuration reveal that the conventional method cannot give a correct prediction of prompt NO and thermal NO, particularly at high air temperature. A method using the concept of fixed nitrogen is presented. Numerical results indicate that the formation process of prompt NO and thermal NO can be evaluated properly by the present method.     

Effect of alkali metals on nitrogen oxide emission: Role of Na and its occurrence in coal

High-alkali coal contains relatively high contents of alkali metals, which can be usually released in the form of gaseous chlorides and hydroxides during combustion. The effect of alkali metals on NO formation is analyzed in an electrical heated drop-tube furnace at 800–1200 °C during coal combustion. Based on experiments and simulations, the mechanisms underlying the effects of Na salts on NO emission are clarified in CO/NH₃/O₂/H₂O/Na additive (NaCl, Na₂SO₄, and NaAc) systems. The results indicate that the yield of NO initially increases and then decreases as the furnace temperature increased. As the temperature increased from 800 to 1000 °C, NO precursors (HCN and NH₃) undergo accelerated oxidation to form NO. When the furnace temperature is greater than 1000 °C, due to the rapid precipitation of volatiles, a local reducing atmosphere is present around the pulverized coal particles, which inhibits NO formation. NaCl and NaAc addition significantly inhibit NO formation. However, the inhibitory effect is weakened at higher temperatures (>1000 °C). The Na₂SO₄ additive exerts little effect on NO generation during combustion because of its stable chemical properties. The same conclusion is also obtained from gaseous experiments showing that NaCl and NaAc significantly inhibit NH₃ oxidation to form NO. Based on the results of calculations, NaCl and NaAc addition inhibits NO formation by promoting the recombination of H, O and OH and reducing the concentrations of radicals. According to the analysis of chemical reactions, the effect of NaCl and NaAc on NO formation is mainly determined by the competitive relationships among multiple reactions.