水蒸气对oxy-coal燃烧中NO生成的影响

为了研究H₂O对燃料N向NO转化各个阶段的影响,采用可沿程取样的沉降炉反应器,研究了一种烟煤在1273 K温度下,O₂/N₂、O₂/CO₂以及O₂/CO₂/H₂O气氛下燃烧的燃尽与NO生成的情况.并通过在停留时间为0.2、0.3、0.5、1.1 s与O₂浓度为5%、21%及30%情况下的实验来研究H₂O对NO生成的影响.实验结果表明,相对于O₂/CO₂气氛,H₂O的添加抑制了NO的生成,且该影响主要集中在燃烧初期挥发分N的氧化过程.随着O₂浓度的增加,H₂O添加对oxy-coal燃烧方式下NO生成影响加大.     

基于Langmuir-Hinshelwood动力学解析O2/CO2/H2O气氛下烟煤焦反应机理

流化床富氧燃烧湿烟气循环兼具经济与环保优势。湿烟气循环（O₂/CO₂/H₂O）条件下煤焦与O₂、CO₂及H₂O的反应同时发生。为探究O₂/CO₂/H₂O气氛下煤焦-O₂、煤焦-CO₂、煤焦-H₂O反应间的相互作用机制,在自制高精度热重实验装置上系统考察了O₂、CO₂、H₂O及其混合气氛下,典型烟煤焦在900℃的反应特性。基于吸附和脱附原理的Langmuir-Hinshelwood（L-H）机理性模型分别计算了烟煤焦与O₂、CO₂和H₂O反应的动力学参数。通过采用单独活性位点与竞争活性位点两种假设分析了O₂/CO₂、O₂/H₂O和CO₂/H₂O气氛下烟煤焦-O₂、烟煤焦-CO₂和烟煤焦-H₂O两两反应间的作用机制,揭示了H₂O分子优先吸附于烟煤焦表面活性位点,O₂分子次之,而CO₂分子相对滞后。O₂/CO₂/H₂O气氛下烟煤焦-O₂、烟煤焦-CO₂、烟煤焦-H₂O反应表现出部分竞争反应活性位点,传统的单独活性位点与竞争活性位点假设均无法准确描述其反应速率特性。基于H₂O分子优先,O₂分子次优先吸附的原理,建立了O₂、CO₂、H₂O混合气氛下煤焦反应速率L-H动力学方程,方程计算结果与实验值良好吻合。研究结果为深入分析煤焦颗粒流化床富氧燃烧特性及构建可靠、准确的燃烧反应模型提供了理论支撑。     

不同烟气组分对粉状活性焦吸附汞的影响机理

在模拟燃煤热烟气为热源和介质条件下，以准东褐煤为原料，通过一维沉降炉进行炭化活化（一步法）制备粉状活性焦，考察了活性焦对Hg⁰的吸附能力，探索了SO₂、H₂O、O₂、CO₂、H₂O+O₂、SO₂+O₂及H₂O+SO₂+O₂气氛对活性焦吸附Hg⁰的影响机理。结果表明：一步法获得的活性焦对Hg⁰具有较高的吸附性能。N₂气氛作对比，H₂O、H₂O+O₂、CO₂和SO₂气氛下抑制活性焦对Hg⁰的吸附；O₂、SO₂+O₂和H₂O+SO₂+O₂促进活性焦对Hg⁰的吸附。通过Hg 4f的XPS分析证明了不同气氛组成对活性焦吸附Hg⁰的抑制和促进机理。H₂O覆盖在活性焦活性位上和堵塞孔隙而抑制活性焦对Hg⁰的吸附；SO₂与Hg⁰在活性焦上发生竞争吸附而抑制对Hg⁰的吸附；CO₂ 吸附在活性焦微孔上而抑制对Hg⁰的吸附；O₂气氛下主要形成了HgO, SO₂+O₂气氛下Hg⁰被氧化成HgSO₃，进一步氧化成HgSO₄； H₂O+SO₂+O₂气氛下，Hg⁰被氧化成HgO和HgSO₄。     

O2/H2O燃烧方式下石灰石的间接硫化反应特性

利用水平管式炉和热重实验台架,对O₂/H₂O、O₂/N₂和O₂/CO₂ 3种不同燃烧方式下石灰石的间接硫化反应特性进行了研究。重点探究了燃烧方式、水蒸气浓度对石灰石间接硫化反应的影响规律与机理。同时,对硫化产物进行了X射线荧光光谱（XRF）、X射线衍射（XRD）、孔结构特性和扫描电镜（SEM）分析。结果表明,O₂/H₂O燃烧方式相比于相同氧浓度下的O₂/N₂和O₂/CO₂燃烧方式,石灰石间接硫化反应的钙转化率在化学反应控制阶段基本相同,在扩散控制阶段O₂/H₂O燃烧方式下的钙转化率有显著的提高。主要原因是水蒸气促进了硫化反应后期产物层内的固态离子扩散。此外,O₂/H₂O燃烧方式下,不同的水蒸气浓度对石灰石的钙转化率基本没有影响。     

干馏层气氛对半焦结构及其CO2气化活性影响

固定床煤气化炉中气氛对干馏层生成半焦的活性影响较大。对不同气氛下制得的半焦进行了CO₂气化活性实验，并采用拉曼光谱和氮吸附对半焦进行了表征。结果表明：与N₂气氛下制得的半焦相比，通入其他气体可以提高半焦的CO₂气化活性，单组分中H₂O气氛下制得的半焦的CO₂气化活性最强，双组分中CO₂+H₂和CO+H₂O气氛下制得的半焦的气化活性明显增加，而且双组分气氛下的CO₂气化活性比前者强；半焦比表面积的增加有利于其CO₂气化活性的提高，但半焦化学结构的变化对其CO₂气化活性的提高作用更明显。     

热解气氛对稻秆半焦组成及气化活性的影响

通过热解装置和热重仪分别研究了不同气氛（N₂、H₂和CO₂）对稻秆热解产物及半焦气化活性的影响。三种气氛中热解半焦产率为CO₂>N₂>H₂,焦油和气体产率为CO₂22;半焦中氧元素含量大小为CO₂>N₂>H₂,说明氢气中热解稻杆的脱氧效果最好;半焦中有机质相对百分含量随热解温度的升高而减小,并且CO₂>N₂>H₂,挥发分占总有机质的百分含量变化趋势与半焦中相反;K和Na析出率为CO₂22;半焦比表面积、孔容和孔径大小顺序为CO₂22;三种...     

乙醇胺对介质阻挡耦合电晕放电同时脱除NO、SO2的影响

采用自行设计的介质阻挡耦合电晕放电等离子体反应装置进行了模拟烟气同时脱硫脱硝的研究,分别考察乙醇胺（HOCH₂CH₂NH₂,MEA）在不同模拟烟气体系中对NO、SO₂脱除的影响,深入探讨了MEA在放电过程中与NO的作用机理。结果表明：在N₂/O₂/SO₂/NO体系中,0.56% MEA的加入可以显著消除O₂对NO脱除的抑制作用;在N₂/CO₂/SO₂/NO体系中,MEA会吸收进入体系中的部分CO₂,以减弱CO₂对NO脱除的抑制;在N₂/O₂/CO₂/H₂O/NO/SO₂体系中,0.56% MEA的加入既可以有效减弱H₂O的影响,也可以使NO的脱除率达到71.28%,继续将MEA的体积分数增大至1.20%时,可将该体系下NO脱除率提高到81.25%;同时,MEA可以在短时间内高效吸收体系内的SO₂,且几乎不受其他气体成分的影响,SO₂脱除率保持在95%左右。     

低湿CO2/H2O混合气体吸附特性实验

CO₂捕集、封存及利用是实现“双碳”目标的重要途径,为将碳捕集后的低湿CO₂/H₂O进行CO₂提纯和资源化利用,采用动态吸附实验研究了不同温度（303K、313K）、H₂O含量（0.7%~3.0%）的CO₂/H₂O在活性炭、活性氧化铝、分子筛3A和13X四种吸附剂上的动态吸附穿透曲线、吸附床温度分布、吸附量,分析了CO₂/H₂O分离系数和吸附热。结果表明,在CO₂/H₂O动态吸附过程中,吸附床温度与各组分浓度随时间变化趋势相同。H₂O饱和时间随进气温度升高而缩短;H₂O含量增加,抑制CO₂吸附;活性炭和氧化铝中H₂O的饱和时间随H₂O含量增加而增长,但分子筛3A和13X饱和时间缩短。H₂O吸附量随H₂O含量增加而增加,吸附热随吸附量增加而减小,CO₂则相反。分子筛3A对CO₂吸附量最小且CO₂/H₂O分离系数最大。H₂O含量小于1%时,CO₂吸附量最大的分子筛13X分离系数大于活性氧化铝,分子筛3A和13X适合分离低湿CO₂/H₂O。     

褐煤氧化和气化反应协同作用下夹带流反应器的建模

为了建立?80mm×3000mm下行夹带流煤气化反应器模型,以胜利褐煤为原料,在该反应器中进行了N₂、O₂、H₂O、H₂O+O₂气氛下800℃/900℃气化实验,研究了流场分布、主要反应发生区域,并结合反应机理和缩合模型推导了不同速控步/气化气氛下C-O₂氧化和C-H₂O气化速率方程。结果发现,实验条件下,喷嘴附近的射流区及其周围的回流区仅占反应器高度的5%,气相主要以平推流流动;热解和燃烧反应同时发生,反应器分为热解燃烧区和气化区;气膜扩散控制下的C-O₂氧化速率方程和化学反应控制时C-H₂O气化速率方程与实验数据吻合较好;相对H₂O气氛,H₂O+O₂气氛下C-H₂O气化反应的表观气化反应速率常数明显较大,尤其在高温下,建模时需分别考虑H₂O和H₂O+O₂气氛下气化速率。这主要是由于氧化反应的开孔/扩孔作用使碳颗粒微孔数量、比表面积、孔容增加,促进了C-H₂O气化反应。采用MATLAB编程拟合求解模型中未知参数和模型,对12组实验（60个数据点）进行预测,85%预测值误差小于20%,70%预测值误差小于10%。对褐煤转化率的预测,75%预测值误差小于4.6%。建立的反应器模型误差较小,为反应器设计和放大奠定基础。     

铁精粉还原炉用Si3N4（Sialon）/SiC材料在H2O—H2—N2气氛中热力学计算分析

根据热力学原理对Si—C—N—H—O五元系统进行了平衡状态下的相稳定性计算,绘制了在1 073 K和1 223 K下的SiC、Si₃N₄、Si₂N₂O和SiO₂4个稳定相的稳定性与N₂分压和H₂O分压的关系图,即优势区域图,分析了其凝聚相的稳定区域。同时结合SEM显微结构分析氢气还原炉中Si₃N₄/SiC和Sialon/SiC制品抗H₂O—H₂—N₂气氛的侵蚀性能。     

Role of active oxygen transients in selective catalytic reduction of N2O with CH4 over Fe-zeolite catalysts

Sharp NO and O₂ desorption peaks, which were caused by the decomposition of nitro and nitrate species over Fe species, were observed in the range of 520–673 K in temperature-programmed desorption (TPD) from Fe-MFI after H₂ treatment at 773 K or high-temperature (HT) treatment at 1073 K followed by N₂O treatment. The amounts of O₂ and NO desorption were dependent on the pretreatment pressure of N₂O in the H₂ and N₂O treatment. The adsorbed species could be regenerated by the H₂ and N₂O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N₂O with CH₄. However, the reaction rate of CH₄ activation by the adsorbed species formed after the H₂ and N₂O or the HT and N₂O treatment was not so high as that of the CH₄ + N₂O reaction over the catalyst after O₂ treatment. The simultaneous presence of CH₄ and N₂O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N₂O dissociation can activate CH₄ in the SCR of N₂O with CH₄.     

Catalytic reduction of NOx with H2/CO/CH4 over PdMOR catalysts

Conversion of NO_x with reducing agents H₂, CO and CH₄, with and without O₂, H₂O, and CO₂ were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NO_x to N₂ conversion with H₂ and CO (>90% conversion and N₂ selectivity) range under lean conditions. The formation of N₂O is absent in the presence of both H₂ and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H₂ and CO at 450–500 K. The positive effect of cerium is significant in the case of H₂ and CH₄ reducing agent but is less obvious with H₂/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673 K in a feed with 2500 ppm CH₄, 500 ppm NO, 5% O₂, 10% H₂O (0–1% H₂), N₂ balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NO_x reduction with H₂, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673 K.     

Partial oxidation of methane by O2 and N2O to syngas over yttrium-stabilized ZrO2

Catalytic partial oxidation of methane to synthesis gas over ZrO₂ and yttrium-stabilized zirconia (YSZ) is studied using O₂ and N₂O as oxidants. ZrO₂ is much more active than YSZ in oxidation of methane with N₂O. In contrast, YSZ is significantly more active than ZrO₂ when O₂ is used as an oxidant. The presence of O₂ does not influence the rate of N₂O decomposition over ZrO₂ and YSZ, while the presence of H₂O in the system decreases N₂O conversion significantly. O₂ and N₂O are activated at different active sites. Y-induced oxygen vacancies are active for O₂ activation, whereas oxygen co-ordinatively unsaturated Zr cations (Zr-CUS) located at corners, edges, steps and kinks are responsible for N₂O activation. These sites are also capable of dissociating H₂O, resulting in competition between H₂O and N₂O. As compared with N₂O, molecular O₂ is easier to be activated over YSZ and ZrO₂.     

Oxidation and reforming reactions of CH4 on a stepped Pt(5 5 7) single crystal

The oxidation and reforming kinetics of methane by O₂, CO₂ and H₂O were studied on a stepped Pt(5 5 7) single crystal from 623 to 1050 K under methane rich conditions. The rate of carbon deposition was followed by ex-situ Auger electron spectroscopy under non-oxidative conditions. The apparent activation energy for methane decomposition was significantly lower than the apparent barriers measured for both total oxidation, CO₂ and H₂O reforming. Total oxidation of methane to CO₂ and H₂O followed by combined dry and steam reforming (combined combustion-reforming) led to CO production rates which were higher than direct CO₂ or H₂O reforming rates. The enhanced rates are most likely due to the ability of adsorbed oxygen to prevent carbon nucleation and/or scavenge carbon enabling the reforming reaction to turnover on a larger fraction of sites. Comparable amounts of carbon were found by Auger electron spectroscopy measurements after both direct dry or steam reforming, while combined oxidation-reforming had considerable less carbon. During direct dry or steam reforming, CO₂ and H₂O serve only to scavenge adsorbed atomic carbon, while in the presence of oxygen, carbon is removed by both combustion and reforming routes.     

Effects of selective reduction of nitric oxide on zeolite structure

The chemical changes that occurred in a Cu-ZSM-5 catalyst during the selective reduction of NO with i-C₄H₁₀ in the presence and absence of O₂ were catalogued. In the presence of excess O₂ complete conversion of the NO to N₂ and the hydrocarbon to CO₂ and H₂O occurred and the Cu²⁺ concentration estimated from the integrated intensity of the electron paramagnetic resonance (EPR) signal was not significantly changed from its initial value. When the oxygen concentration was lowered below the point of stoichiometry, however, both of these conversions decreased modestly, but when O₂ was eliminated from the feed both conversions fell precipitously and the acid catalyzed decomposition products of isobutane appeared in the products instead of CO₂ and H₂O. These changes were accompanied by corresponding changes in the EPR data. Lowering the O₂ below the point of stoichiometry effected a loss of from 30% to 50% of the intensity of the Cu²⁺ signal. Eliminating O₂ reduced the signal by several orders of magnitude. Remarkably, these reduced catalysts could be restored to their initial oxidation states by adding excess O₂ into the feed stream, even when there was evidence that Cu⁰ was present. Dealumination accompanied selective reduction even in excess O₂, particularly above 623 K. This was probably caused by steaming of the catalyst by the H₂O produced in the reaction.