O_2/CO_2气氛下煤粉燃烧特性及动力学分析

采用热重实验系统进行了煤粉在O_2/N_2和O_2/CO_2气氛下的燃烧实验,研究了氧体积分数和粒径对燃烧特性的影响.实验结果表明,氧体积分数越高、粒径越小,煤粉的燃烧特性越好.在氧体积分数较高时,煤粉在O_2/CO_2气氛下的反应比在O_2/N_2气氛下进行得慢;而氧体积分数较低时,煤粉在O_2/CO_2气氛下的反应比在O_2/N_2气氛下进行得快.此外,采用Coats-Redfern积分法、Flynn-Wall-Ozawa积分法和Kissinger-Akahira-Sunose积分法对煤粉在程序升温过程中的燃烧反应做了相应的动力学分析.结果表明,O_2/N_2和O_2/CO_2气氛下不同氧体积分数时的煤粉燃烧反应动力学参数表观活化能E和指前因子A之间具有动力学补偿效应.煤粉燃烧过程中在同一转化率下的表观活化能E随其粒径的减小而降低.     

典型煤种O_2/CO_2/H_2O气氛下中高温燃烧时NO的生成特性

利用自制恒温热分析系统研究了大同烟煤和阳泉无烟煤在O_2/CO_2/H_2O气氛下中高温燃烧时NO的释放行为,并与O_2/N_2和O_2/CO_2气氛下的情况进行了对比分析.结果表明:当氧气体积分数为5%时,大同烟煤在O_2/CO_2和O_2/N_2气氛下燃烧时只有一个NO体积分数峰,而在O_2/CO_2/H_2O气氛下却变成一前一后2个峰;当氧气体积分数升高到21%后,大同烟煤在O_2/CO_2/H_2O气氛中的NO释放过程又变为一个体积分数峰;阳泉无烟煤的NO释放过程与大同烟煤类似;大同烟煤在O_2/CO_2气氛中的NO排放量始终低于O_2/N_2气氛中;由于低氧气体积分数下H_2O气化反应的影响,大同烟煤在O_2/CO_2/H_2O气氛中的NO排放量在高温下高于O_2/CO_2气氛中;氧气体积分数升高后,大同烟煤在O_2/CO_2/H_2O气氛中的NO排放量又低于O_2/CO_2气氛中;阳泉无烟煤的NO排放量高于大同烟煤,但其不同气氛下的变化趋势与大同烟煤一致.     

基于O2/CO2气氛的煤粉燃烧性能研究

采用热重分析法研究富氧燃烧(O_2/CO_2)气氛、O_2体积分数和煤粉活性对褐煤、烟煤、无烟煤3种煤粉燃烧性能的影响,并进行分温度区间的燃烧反应动力学分析。结果表明:褐煤和无烟煤发生非均相着火,烟煤发生均相-非均相着火;相比空气气氛,O_2体积分数相同的O_2/CO_2气氛下煤粉的着火温度和燃尽温度升高,燃尽时间延长;在O_2/CO_2气氛下,当O_2体积分数增大时,煤粉着火温度和燃尽温度降低,燃尽时间缩短;相同气氛下,煤粉活性显著影响其着火和燃尽;根据综合燃烧特性指数判断,增大O_2体积分数显著改善了煤粉的燃尽特性;在低温区,煤粉燃烧属于0.3级反应,在高温区则为1～2.5级反应。     

低氧稀释条件下煤粉颗粒燃烧特性实验研究

在平面扩散火焰煤粉燃烧实验系统上采用光纤光谱仪和CMOS相机分别测量了不同燃烧气氛(O_2/N_2、O_2/CO_2)、热协流温度(1 473～1 873 K)和氧气体积分数(5%～20%)下烟煤煤粉燃烧火焰的辐射光谱和火焰图像,获得了不同燃烧条件下煤粉颗粒温度沿程分布和燃烧特性。结果表明:在O_2/N_2或O_2/CO_2气氛下,随着热协流温度和氧气体积分数的降低,火焰颜色由亮黄色逐渐转变为暗红色,煤粉颗粒温度降低;随着热协流氧气体积分数的下降,煤粉颗粒温度波动系数减小了37%,颗粒温度分布更均匀;与O_2/N_2气氛相比,O_2/CO_2气氛下煤粉火焰光强减弱,煤粉着火距离增加,煤粉颗粒的平均温度降低了24～103 K,颗粒温度波动系数最大减小了24%。     

CO2/N2气氛下煤粉热解气化特性研究及动力学分析

采用热重分析仪在CO_2/N_2气氛下对煤粉进行了非等温热解气化实验研究,分析了程序升温速率和CO2浓度对煤粉热解、气化特性的影响,并采用Coats-Redfern法、FWO法和KAS法对煤粉热解、气化过程进行了动力学分析。实验结果表明:在CO_2/N_2气氛下,随着程序升温速率的升高,热解和气化反应速率均增大,表观活化能均减小。在CO_2/N_2气氛下,CO2不会影响煤粉的热解过程,而对气化过程有决定性影响,CO2浓度越高,气化反应速率越大,表观活化能越大。在CO_2/N_2气氛中煤粉气化反应的表观活化能E和表观指前因子A之间具有动力学补偿效应。在相同气氛下,煤粉气化反应的表观活化能随转化率的增大而减小。     

添加CO_2/H_2O对正丁醇火焰中碳烟反应的影响

耦合简化的正丁醇动力学机理和固定分区碳烟模型,研究了在空气中添加CO_2或H_2O蒸气对正丁醇同轴扩散火焰中碳烟质量分数和数密度的影响,计算结果表明:添加CO_2或H_2O蒸气后,整体上二者均降低;此外,添加CO_2后各反应与组分生成往火焰下游移动.碳烟数密度的降低是由于温度和苾(A4)浓度降低引起的成核速率的下降,而碳烟质量分数的降低主要是由于H摩尔分数、颗粒总表面积及温度降低引起的脱氢加乙炔(HACA)速率的下降.碳烟最终在火焰下游被完全氧化,主要氧化组分为OH.     

水蒸气浓度对层流甲烷扩散火焰中碳烟生成的影响

对甲烷在氧—汽燃烧过程中碳烟生成状况进行了数值模拟研究。通过对比O_2/N_2和O_2/H_2O氛围下四种工况(21%O_2、30%O_2、40%O_2、50%O_2)的火焰形态和碳烟体积分数,发现相同O_2浓度下,前者火焰温度、火焰高度、碳烟体积分数均低于后者,表明H_2O能够明显抑制碳烟生成。通过对比O_2/N_2、O_2/H_2O和O_2/FH_2O氛围下四种工况的最大碳烟体积分数和最大颗粒数量密度,表明不仅H_2O的化学效应抑制碳烟生成,而且其他三大效应也共同抑制碳烟生成。通过进一步分析化学效应随H_2O浓度的变化规律,确定了H_2O浓度为60%时,化学效应的抑制效果最佳。     

NO2-O2气氛下柴油机碳烟氧化特性及氧化机理

通过热重分析仪及无模式函数法研究了柴油机碳烟在O_2、NO_2-O_2气氛下的氧化特性及氧化机理,并探究了NO_2对碳烟氧化反应的影响机制.结果表明:在10%O_2中添加0.1%NO_2降低了柴油机碳烟氧化反应的起燃温度和燃尽温度,并且NO_2对上述氧化反应特征温度的影响效果随升温速率(10℃/min、12℃/min、15℃/min)的增加而提高;添加0.1%NO_2促进柴油机碳烟氧化反应的进行,显著降低氧化反应本征活化能;柴油机碳烟氧化过程可分成氧化前期、氧化中期及氧化后期3个阶段;随碳烟失重比的增加,碳烟氧化反应有效活化能先增后减再不变,其原因为本征反应和气体扩散作用对氧化速率影响效果的此消彼长;碳烟失重比小于65%时,NO_2能够降低碳烟氧化反应有效活化能,碳烟失重比大于等于65%时,NO_2对有效活化能的影响逐渐消失.     

柴油机颗粒物热重参数优化选择及其氧化特性研究

探究了柴油机颗粒物中可溶有机成分(soluble organic fraction,SOF)及热重参数对碳烟氧化特性的影响,并基于Coats-Redfern算法得到不同升温速率下碳烟的氧化动力学参数。研究结果表明:在碳烟缓慢氧化阶段,柴油机颗粒中SOF组分阻碍了碳烟氧化反应的进行,而脱SOF后碳烟比表面积增大,更利于氧化反应的进行。与脱SOF前相比,脱SOF后相应的氧化特征温度均有所降低,因而颗粒物去除SOF后的热重试验更能反应碳烟的氧化动力学特性。通过比较试验,确定进样量、工作气流量和升温速率等热重参数的优化取值,其中升温速率对碳烟氧化燃烧反应的影响显著。随着升温速率增大,碳烟氧化反应出现滞后现象,其特征温度升高且最大失重率峰值降低,而升温速率对碳烟热解程度和氧化反应温度区间大小无明显影响。通过对比分析,低升温速率(3℃/min)条件下扩散控制可以忽略不计,氧化特征温度重复性最好。不同升温速率下碳烟燃烧反应动力学参数活化能E和指前因子A之间存在动力学补偿效应,E与A均随升温速率的降低而减小。     

基于碳氧原子比空间的富氧燃烧火焰结构及碳黑初生分析

针对富氧C_2H_4/O_2/N_2和C_2H_4/O_2/CO_2对冲火焰,采用详细的化学反应机理进行了数值模拟,在碳氧原子比(C/O)空间下分析了火焰结构和碳黑颗粒初生以及CO_2代替空气中的N_2对碳黑初生的影响.结果表明:在O_2/N2和O_2/CO_2气氛下,随着化学计量混合分数(Zst)的增加,C/O空间下对冲火焰的火焰面位置不变,对应的C/O_原子比值分别为0.50、0.53.在C/O_空间下,两种气氛下,随着Zst的增加火焰中C_6H_6出现的位置不变,C/O原子比值都为0.47左右.当用CO_2代替空气中的N_2时,火焰温度降低,同时使CO_+OH■CO_2+H的逆反应增强,导致火焰中的C_2H_2、H的摩尔分数减少,OH的摩尔分数增加,抑制碳黑的初生.     

Evaluation of in-situ formed La2O3–TiO2–La2O2CO3 nanocomposite photocatalyst for H2 production

The photocatalytic evolution of H₂ over La₂O₃ decorated TiO₂ catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La₂O₃/TiO₂ into La₂O₃–TiO₂–La₂O₂CO₃ occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H₂ yield. The 2 wt%La₂O₃/TiO₂ nanocomposite demonstrated better H₂ yield (～8.76 mmol (g_cat)^?1) than the bare TiO₂ (～1.1 mmol (g_cat)^?1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H₂ rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H₂-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy.     

Photocatalytic H2 production over RuO2@ZnS and RuO2@CuS nanostructures

Photocatalytic hydrogen production is a promising approach of sustainable economy, because a use of sunlight and water to produce a fuel will solve a problem of fossil fuels depletion. Metal sulfides are well known photocatalysts in water splitting process, but in absence of sacrificial electron donor they undergo a photocorrosion. In this paper we studied a possible strategy to protect the sulfide photocatalysts and to improve its photostability by a deposition of small amount of ruthenium oxide at surface of sulfides. Nanocrystalline zinc sulfide and copper sulfide were prepared in a hydrothermal way and have been functionalized by RuO₂. As prepared photocatalysts showed good activity towards hydrogen formation. Modification of sulfides with ruthenium oxide had a few positive effects: it expanded a light absorption range by photocatalysts, enhanced the photocatalytic activity towards H₂ formation, improved a photostability in comparison with neat ZnS and CuS as well as protected from the electronic and structural changes within semiconductors due to irradiation.     

Numerical study of the O2/CO2, O2/CO2/N2, and O2/N2-syngas MILD combustion: Effects of oxidant temperature,O2 mole fraction,and fuel blends

Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (T_ox), and oxygen mole fraction (X_O2) are selected as the main parameters. Fake species (FCO₂) with the same CO₂ physical properties is used for separation the physical and chemical effects of replacing CO₂ with N₂. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N₂ to CO₂ is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all X_O2, the physical and chemical effects of replacing CO₂ with N₂ have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO₂ and N₂ play a key role on IDT enhancement by increasing CO₂ in the oxidant composition. The sensitivity analysis of CH₂O for variations of T_ox and X_O2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion.     

Photocatalytic reduction of CO2 using TiO2 powders in supercritical fluid CO2

The photocatalytic reduction of CO₂ was investigated using TiO₂ powders in supercritical fluid CO₂. These were irradiated in a stainless steel vessel at 9.0 MPa and 35°C. After reducing the CO₂ pressure to the ordinary state, pure water was added to the vessel while avoiding air contamination. No gaseous reduction products were observed. Formic acid was obtained only in aqueous solution. The optimal irradiation time for the production of formic acid was 5 h. Addition of acidic solutions rather than pure water was preferable for formic acid formation. Formic acid seems to be produced through the protonation of reaction intermediates on TiO₂ powders in solutions. The CO₂-reduction system described here may be of practical value for efficient CO₂-conversion and fixation, storage of solar energy, and production of raw materials for the photochemical industry.     

保护气氛烧结炉

介绍了HIC封装管壳中玻璃绝缘子网带烧结炉的特殊机械结构、氮氢保护气氛系统和电气保护措施。确立了网带炉低速爬行力学模型及炉内合理的气氛流向。     

New gas chromatographic packing ZIF-67@NH2–SiO2 for separation of hydrogen isotope H2/D2

ZIF-67@NH₂–SiO₂ composites were prepared by loading the metal-organic frameworks ZIF-67 on amino modified SiO₂ gel particles (NH₂–SiO₂, 80–100 mesh) through layer-by-layer self-assembly method. Systematic investigation on the effects of ZIF-67 loading amounts on NH₂–SiO₂ packed stainless steel chromatographic column (specification 1.0 m×2.0 mm I.D.), the flow rate of He as carrier gas and the injection amount of mixed gas (H₂/D₂) on the hydrogen isotope H₂/D₂ separation performance at liquid nitrogen temperature, unraveled the optimal conditions for H₂/D₂ isotope separation. The results showed that the optimal stationary phase materials under the optimized conditions can effectively separate H₂ and D₂ with separation resolution R = 1.52 and the separation time t = 10.15 min. The superior performance of the ZIF-67 is tentatively thought to be due to kinetic quantum sieving (pore size 3.3 Å) effect and chemical affinity sieving effect of Co ion in ZIF-67.