预热空气当量比对循环流化床掺混煤泥预热燃烧的影响

煤泥灰含量大、颗粒细、热值低,煤泥的高效清洁燃烧是固废资源化利用的重要方式之一。采用煤粉流态化预热耦合循环流化床燃烧技术,在30 kW预热燃烧综合评价试验台上,控制煤泥掺混比、给料量、还原区当量比、二/三次风比例及过剩空气系数等参数不变,并借助煤气分析仪和烟气分析仪等测量仪器,开展了循环流化床烟煤掺混煤泥的预热燃烧试验。结果表明,循环流化床预热燃烧系统运行稳定可靠,预热温度800℃以上,预热燃料可持续稳定输送到循环流化床中;烟煤掺混高灰分的煤泥,循环灰量增加,循环流化床燃烧室温差小,温度均匀;预热空气当量比由0.36增至0.51时,预热器内温度增加,预热煤气中CO₂、HCN体积分数增加,CO、H₂、CH₄及NH₃体积分数降低,煤气热值由2.02 MJ/m³降至1.49 MJ/m³;且随着预热空气当量比的增加,循环流化床燃烧室沿程NO体积分数增加,CO体积分数底部高、上部低,NO_x排放量由172 mg/m³增至24...     

烧结烟气中成分对焦炭还原NO影响的实验研究

利用烧结烟气循环流化床燃烧的深度净化技术,可低成本、高效地实现烧结烟气中污染物的超低排放。为了探究该技术中循环流化床密相区内焦炭还原NO的机理,以焦作无烟煤所制焦炭为实验对象,利用高温立式管式炉实验台模拟循环流化床密相区,在750℃～950℃温度下,研究烧结烟气中分别加入组分CO,CO₂,O₂时,焦炭还原NO的转化率随时间变化规律。结果表明：在无O₂通入的反应条件下,随着反应温度的提高,焦炭对NO的还原率逐渐增加;CO的加入提升了焦炭对NO的还原率,在反应温度为900℃时,加入体积分数为0.4%的CO可最大提升17%的NO还原率;CO₂的加入则抑制了焦炭对NO的还原率,在反应温度为950℃时,加入体积分数为10%的CO₂使得NO还原率最大降低了21%;O₂的加入明显抑制了焦炭对NO的还原效果,在反应温度为950℃,通入气体中体积分数为13%的O₂时,NO的还原率下降至31%,且明显缩短了焦炭的还原时间。研究结果可为烧结烟气循环流化床燃...     

低温燃烧下NH3的氧化特性

NH₃的气相氧化是低温燃烧过程中NO_x（NO和NO₂）与N₂O的重要来源,为了深入认识其反应规律,在管式流动反应器系统中进行了实验研究。重点考察了挥发分中的可燃气（CO、CH₄或H₂）和NO对NH₃氧化及氮氧化物排放的影响规律,并根据化学反应机理对实验结果进行了分析。研究结果表明,低温氧化性气氛下微量的可燃气就能够显著促进NH₃的氧化,并使NO_x和N₂O的生成量大幅度升高。当可燃气体浓度相同时,H₂对NH₃氧化的影响最大,CO的影响最小,CH₄对NH₃氧化的影响略大于CO。随着可燃气体浓度的升高,其对NH₃氧化与氮氧化物生成的影响先逐渐增加,然后趋于稳定。反应初始气体中存在NO时,也会加速NH₃的氧化。     

15 MW生物质循环流化床NOx和温室气体排放特性

生物质是零碳可再生能源，对我国实现碳达峰、碳中和目标具有重要意义。虽然被视为清洁能源，但生物质燃烧过程仍会排放NO_x(NO、N₂O)和温室气体(CH₄、N₂O、CO₂),有必要对生物质直燃的NO_x和温室气体排放特性进行研究。测量某15 MW生物质循环流化床的NO_x和温室气体排放，并探究了改变床压、一二次风比、前后墙二次风比、废木料掺烧比例等因素对NO_x和温室气体排放特性的影响。燃烧调整试验表明：升高床压有利于降低NO排放，但降幅很小，且会造成CO和CH₄体积分数上升，CO₂体积分数降低；随一二次风比增大，NO排放略降低，这意味着可适当降低二次风以降低NO排放量，CO和CH₄体积分数降低，CO₂体积分数升高；当前墙二次风开度/后墙二次风开度较小或较大时，均有利于降低NO,CO和CH₄排放量也较低；高含氮废木...     

低温等离子体用于柴油机尾气脱硝的实验

柴油机作为卡车、重型机械以及船舶的主动力装置仍被广泛采用,其尾气中氮氧化物的脱除技术也是目前的研究热点。本文搭建了模拟柴油机尾气的配气系统,采用介质阻挡放电产生低温等离子体（non-thermal plasma,NTP）的方法对模拟柴油机尾气进行了脱硝的实验研究。实验结果表明：针对本系统,电源效率和能量密度随着输入电压的增大而升高,当输入电压高于60V时,电源效率在90%以上;在O₂/N₂条件下,随着O₂浓度以及能量密度的增加,NO生成量逐渐增加,NO₂生成量先增加后降低最终趋于稳定;在NO/N₂条件下,低温等离子体对NO的脱除率接近100%;在NO/O₂/N₂条件下,随着NO浓度的增加,临界O₂浓度升高,O₂体积分数为1%时脱硝效率在90%以上,O₂体积分数高于14%时低温等离子体的脱硝率为负值,且随着能量密度的增加,生成的NO _x 浓度也更高,O₂浓度对低温等离子体的脱硝性能起决定性作用;在低能量密度时,加入NH₃会提高脱硝性能,高能量密度时NH₃会略微降低NTP的脱硝性能,当加入H₂O模拟真实柴油机尾气成分且喷氨时,获得的脱硝率最高为40.6%。     

基于热重-质谱联用的煤粉富氧燃烧动力学及污染物生成特性

富氧燃烧是最具工业化前景的燃烧中碳捕集技术之一,为更深入掌握煤粉富氧燃烧的着火模式和污染物生成特性,本文构建了热重-质谱联用实验系统,以烟煤和无烟煤标准煤样为对象,针对3个不同的氧气体积分数：21%、30%和50%,研究了O₂/Ar和O₂/CO₂气氛下煤粉的富氧燃烧特性。结果表明,O₂/CO₂气氛下煤粉着火温度和燃尽温度均降低,燃烧速率提高,燃烧时间缩短;两种煤粉在O₂/Ar气氛下的燃烧都属于非均相着火,而富氧燃烧都属于均相着火模式;氧气体积分数在30%以上时,无烟煤O₂/CO₂燃烧的表观活化能明显低于O₂/Ar气氛,在相同工况下烟煤的表观活化能均低于无烟煤;O₂/CO₂气氛促进了CO和挥发分NO的逸出,生成温度均低于O₂/Ar气氛,CO会对NO起到还原作用。     

Fe对高温还原区煤焦/NH3还原NO的影响

利用高温管式炉实验系统,研究了高温还原性气氛下煤焦与矿物质Fe对氨气还原NO的影响,其中煤焦包含原煤焦、脱矿煤焦和浸渍铁煤焦三种。结果表明：在均相还原中NO还原效率随着氨氮体积比(V(NH₃)∶V(NO))的增加而增加;1 000℃～1 300℃温度范围内,随着温度的升高,出口NO浓度显著降低,1 400℃～1 600℃温度范围内,出口NO浓度呈现先增加后降低的趋势;原煤焦参与NH₃异相还原NO反应中出口NO浓度较NH₃均相还原NO反应中出口NO浓度低,这是由于原煤焦协同NH₃促进NO的异相还原;相对于原煤焦而言,脱矿煤焦对NH₃还原NO的促进效果更显著,并且NH₃协同脱矿煤焦对NO异相还原的促进作用随着温度的升高而增强;浸渍铁煤焦对NH₃还原NO的过程表现为抑制作用,并且在1 500℃下抑制作用更为明显,其原因为铁与氨基结合为含铁络合物,降低了体系用于还原NO的NH₂/NH自由基浓度。     

添加剂CH3COONH4对介质阻挡-电晕放电耦合法脱除NO、SO2的影响

采用自行研究设计的介质阻挡-电晕放电等离子体反应装置在模拟烟气中进行NO、SO₂的脱除研究。考察了O₂、CO₂、水蒸气等气体组分对脱除NO、SO₂的影响,并进一步探讨了添加剂CH₃COONH₄对脱除NO、SO₂的影响及作用机理。实验结果表明：O₂、CO₂和水蒸气浓度的增加对NO脱除有抑制作用,而引入CH₃COONH₄后,这些抑制作用会被减弱,使NO的脱除率得到大幅度提升,但这些抑制作用不会完全消除。在引入CH₃COONH₄后,气体组分和输入电流的变化对脱除SO₂的影响不明显,SO₂脱除率可达到94%左右。在N₂/O₂/CO₂/H₂O/NO/SO₂体系中加入0.27%的CH₃COONH₄后,NO初始浓度不变的条件下,SO₂含量较少时,对NO的脱除影响不明显,随着SO₂浓度的增加,NO的脱除率不断下降,增加CH₃COONH₄的添加量可消除SO₂的影响;另一方面,在SO₂初始浓度恒定的条件下,随着NO含量的增加,SO₂的脱除率保持在94%左右。在N₂/O₂/CO₂/H₂O/NO/SO₂体系中加入0.51%的CH₃COONH₄后,输入电流2.5A时,NO的脱除率达到72%。     

含氨燃料预混火焰的层流火焰速度及NO排放特性

将甲烷或氢气与氨气共燃可以克服NH₃火焰的点火能量高、燃烧速度慢的缺点。为了解NH₃作为燃料的燃烧特性,对含NH₃燃料进行一维层流预混火焰数值模拟,研究其层流火焰速度及NO排放特性。采用文献中5个简化反应机理进行数值计算,发现Okafor机理模拟NH₃/CH₄/air火焰精度更高;Xiao机理模拟NH₃/H₂/air、NH₃/air精度适中,计算时间较短。此外,开展了当量比、燃料混合物组分比例、压力等参数对含NH₃燃料燃烧时烟气中NO浓度影响的研究。研究发现：含NH₃燃料燃烧时NO主要通过OH、H、O自由基和O₂分子的消耗而生成,主要通过与NH_i（i=0, 1, 2）自由基反应消耗;含NH₃燃料在富燃状态下燃烧可有效减少NO排放,但富燃燃烧效率低,可采用富燃-贫燃分级燃烧技术来提高燃烧效率,同时保持NO的低排放;掺有较多NH₃的含NH₃燃料在中高压下燃烧时可有效减少NO排放。     

城市污泥慢速热解过程中氮的转化规律

利用热重-质谱联用(TG-MS)技术研究城市污泥慢速热解特性及含氮气体产物的生成规律,同时利用原位红外光谱仪实时检测固体表面官能团的变化。研究结果表明:初沉污泥在500℃之前热解已基本完成,二沉污泥由于添加了矿物质盐类,在700℃左右仍有一个较大的失重峰;二沉污泥热解过程HCN和NH₃总生成量均小于初沉污泥,即二沉污泥所加矿物质抑制了HCN和NH₃释放;但温度大于400℃时所加矿物质对HNCO生成具有一定促进作用;污泥中蛋白质热分解会产生环酰胺类物质、含氮杂环化合物和腈类物质,并最终转化为HCN,这是污泥热解过程中HCN的主要来源;400℃以下NH₃主要来自铵盐分解和HCN转化,蛋白质热分解对于NH₃生成贡献很小;400℃以上基本检测不到NH₃生成,即较高温度下挥发分二次反应对NH₃生成几乎没有影响;300~480℃,污泥中木质素裂解产生了大量含氧自由基,促使HCN转化为N₂O,HNCO则最终转化成了NO。     

无烟煤化学链燃烧过程燃料氮转化释放特性

基于赤铁矿石载氧体,在小型单流化床反应器上,开展煤挥发分和焦炭的化学链燃烧研究,探讨挥发分氮和焦氮在化学链燃烧过程中的转化特性。研究表明:燃料氮释放的中间产物HCN和NH₃与铁矿石载氧体具有较高的化学反应亲和性,易于被载氧体氧化生成N₂和NO。淮北无烟煤挥发分氮转化过程中,NO是唯一的氮氧化物,反应器出口中间产物NH₃的释放份额略高于HCN。在煤焦化学链燃烧还原过程中,部分燃料氮释放的中间产物HCN和NH₃被铁矿石氧化导致少量NO的生成,还原过程中无N₂O的释放;较高的还原反应温度加速了NO的生成。减少进入载氧体氧化再生过程的焦炭量可减少空气反应器NO和N₂O的生成。     

SIMULTANEOUS REACTIONS OF CO, NO, O2 AND NH3 ON Pt/γA12O3 CATALYST IN A TUBULAR REACTOR

A reliable method to continuously monitor NH₃ in a gas stream containing CO—NO—O₂ and H₂O has been developed. The method is based on a quantitative oxidation of NH₃ to NO on a Pt catalyst. The extent of this reaction is affected by temperature, excess oxygen present, and space-velocity. There is a significant effect of inlet O₂ concentration on extent of various reactions in the CO—NO—O₂—H₂O system on a Pt/γAl₂O₃ catalyst. At fixed space-velocity and catalyst temperature, and for fixed reactor inlet concentrations of CO and NO. there is negligible CO—NO reaction either in the absence of oxygen or in the presence of excess oxygen. However, short of the stoichiometric amount of O₂ required for CO oxidation, there is appreciable CO—NO (and possibly also CO—NO—H₂O) reaction whose extent increases with increasing oxygen concentration. This increase is especially dramatic in a narrow window of O₂: concentrations near the stoichiometric point. Interestingly enough, near the stoichiometric point, self-sustained isothermal oscillations in the outlet CO and NO concentrations are also observed (Subramaniam and Varma. submitted for publication)     

Study of M-ZSM-5 nanocatalysts (M:Cu,Mn, Fe,Co...) for selective catalytic reduction of NO with NH3: Process optimization by Taguchi method

A series of different transition metals (V, Co, Cr, Mn, Fe, Ni, Cu and Zn) promoted H-ZSM-5 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalytic activity of these catalysts was evaluated for the selective catalytic reduction (SCR) of NO with NH₃ as reductant in the presence of oxygen. The results revealed that the catalytic activity of Cu-ZSM-5 nanocatalyst for NO conversion to N₂ was 80% at 300 ℃, which was the best among various promoted metals. Design of experiments (DOEs) with Taguchi method was employed to optimize NH₃-SCR process parameters such as NH₃/NO ratio, O₂ concentration, and gas hourly space velocity (GHSV) over Cu-ZSM-5 nanocatalyst at 250 and 300 ℃. Results showed that the most important parameter in NH₃-SCR of NO is O₂ concentration; followed by NH₃/NO ratio and GHSV has little importance. The NO conversion to N₂ of 63.1% and 94.86%was observed at 250 ℃ and 300 ℃, respectively under the obtained optimum conditions.     

Alumina- and titania-based monolithic catalysts for low temperature selective catalytic reduction of nitrogen oxides

The selective catalytic reduction of NO+NO₂ (NO_x) at low temperature (180–230°C) with ammonia has been investigated with copper-nickel and vanadium oxides supported on titania and alumina monoliths. The influence of the operating temperature, as well as NH₃/NO_x and NO/NO₂ inlet ratios has been studied. High NO_x conversions were obtained at operating conditions similar to those used in industrial scale units with all the catalysts. Reaction temperature, ammonia and nitrogen dioxide inlet concentration increased the N₂O formation with the copper-nickel catalysts, while no increase was observed with the vanadium catalysts. The vanadium-titania catalyst exhibited the highest DeNO_x activity, with no detectable ammonia slip and a low N₂O formation when NH₃/NO_x inlet ratio was kept below 0.8. TPR results of this catalyst with NO/NH₃/O₂, NO₂/NH₃/O₂ and NO/NO₂/NH₃/O₂ feed mixtures indicated that the presence of NO₂ as the only nitrogen oxide increases the quantity of adsorbed species, which seem to be responsible for N₂O formation. When NO was also present, N₂O formation was not observed.     

Research advance in mechanism of low-temperature SCR of NO on carbon materials

简述了不同反应物组合在碳材料表面的行为特征,单组分NO可以形成吸附态的NO₂、二聚体(NO)₂、—NO₂或吡啶类的化合物;O₂存在时NO被吸附态的氧氧化成NO₂;NO、O₂和NH₃同时存在时,反应发生在吸附态的NH₃和吸附态的NO₂之间。着重详述了活性碳纤维（activated carbon fibers,ACF）催化剂上的选择性催化还原（selective catalytic reduction,SCR）NO的机理为：低温时以NH₃为还原剂的SCR（NH₃-SCR）遵循Langmuir-Hinshelwood机理,较高温度时NH₃-SCR 遵循Eley-Rideal机理;分析指出了催化剂孔结构特征和表面化学官能团是ACF能低温选择性催化还原NO的主要影响因素。     

Effect of fuel composition on the conversion of volatile solid fuel-N to N2O and NO

Older fuels, which generally have a low fuel-O/fuel-N ratio, produce more N₂O in fluidized bed combustion than younger fuels. Here, a proposal is made regarding the effect of fuel composition on the conversion of fuel-N to N₂O and NO through HCN and NH₃ at temperatures typical of fluidized bed combustion. Because earlier experiments have shown that the fuel oxygen plays an important role in fuel-N chemistry, fuel oxygen was considered together with fuel nitrogen. In model compound studies, phenolic OH-groups in particular were found to increase the conversion of HCN to NH₃. In general, the abundance of phenolic oxygen in fuel follows the fuel oxygen concentration. The importance of reactions between OH radicals and HCN was therefore considered.     

Low-temperature selective catalytic reduction of NO with NH based on MnO-CeO/ACFN

MnO_x-CeO_x/ACFN were prepared by the impregnation method and used as catalyst for selective catalytic reduction of NO with NH₃ at 80°C–150°C. The catalyst was characterized by N₂-BET, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The fraction of the mesopore and the oxygen functional groups on the surface of activated carbon fiber (ACF) increased after the treatment with nitric acid, which was favorable to improve the catalytic activities of MnO_x-CeO_x/ACFN. The experimental results show that the conversion of NO is nearly 100% in the range 100°C–150°C under the optimal preparation conditions of MnO_x-CeO_x/ACFN. In addition, the effects of a series of performance parameters, including initial NH₃ concentration, NO concentration and O₂ concentration, on the conversion of NO were studied.