O_2/CO_2气氛下甲烷燃烧中NO_x转化过程的CHEMKIN模拟

采用CHEMKIN中的PFR模型对CH4在不同气氛(O2/CO2和O2/N2)下的燃烧过程进行单程模拟来研究NH3的转化和NOx生成过程,并引入烟气再循环对其进一步模拟来研究实际富氧甲烷燃烧NOx排放机理。结果表明:富燃料燃烧时CO2气氛下的NOx排放比N2气氛高,贫燃料燃烧时2种气氛的NOx排放相当。CO2气氛下,引入烟气再循环后,过氧系数λ=0.7时,NOx排放比单程时降低95%;λ=1.2时比单程降低18%。烟气再循环是导致富氧甲烷燃烧低NOx排放的主要因素。     

空气深度分级燃烧NOx排放特性的CHEMKIN模拟研究

利用两段PFR反应器构建模型在CHEMKIN中模拟,研究空气深度分级燃烧中各个影响因素,使用生成速率分析和敏感性分析,探求燃料N向NO_x的转化路径及原因.模拟结果表明,主燃区α对NO_x转化率影响较大,高温强还原氛围能明显降低NO_x排放;改变燃烧温度降低NO_x排放,应当考虑主燃区,而非燃尽区;当主燃区温度小于1 500℃,燃尽风比率为35%左右时,NO_x排放最低;富燃条件下O_2/CO_2燃烧增大了OH/H,促进NO_x生成;燃尽风位置向后移会降低NO_x转化率,改变燃尽风氧浓度NO_x转化率几乎不变.本文不仅扩大了前人对空气分级燃烧的研究范围,而且对于前人没有研究的影响因素给出了结果,并且进行了化学反应动力学分析,对实际锅炉运行过程中减少NO_x排放具有指导意义.     

辊道窑烧成带火焰空间在富氧气氛下NO_x生成的研究

采用FLUENT软件对气烧明焰陶瓷辊道窑烧成带的火焰空间进行数值模拟研究,对在富氧气氛下以天然气和炉煤气为燃料时辊道窑烧成带的NO_x生成进行分析,并与空气气氛下进行对比。数值模拟结果表明:当燃料种类和燃料量一定时,富氧燃烧可以提高燃烧的火焰温度,w(O_2)由23%升至35%时,各截面温度均升高200～250K,燃烧发生炉煤气时比天然气平均温度高、增幅大。随w(O_2)增加,以发生炉煤气为燃料时炉内NO生成先增后减然后缓慢回升,燃用天然气时,NO持续缓慢增加,但两者w(NO)均持续增大,相比于空气气氛下,分别增长了141.48%和107.73%。以天然气为燃料时炉内NO生成以快速型为主导,以发生炉煤气为燃料时以热力型为主导;富氧燃烧时气氛中的w(NO_x)增加而烟气量减少,采用不同燃料时出口处NO_x生成速率有不同变化。     

链条炉分区段烟气再循环对锅炉运行及NO_x排放特性影响的工业试验

对某台采用尽早配风方式的29 MW锅炉,进行了分段烟气再循环,并对锅炉的运行及NO_x排放特性产生的影响进行了工业试验。在挥发分析出及燃烧区段煤层下的一次风室混入再循环烟气将有效强化该区段煤层燃烧,降低该区段煤层以上燃烧空间的氧浓度,控制及消减挥发分N向NO_x的转化,同时降低了穿过该区段煤层一次风的氧浓度,抑制焦炭N向NO_x转化,NO消减效果最高达到25%。在焦炭燃烧区段煤层下的一次风室混入再循环烟气,能够降低穿过床层气流的氧浓度,抑制焦炭氮向NO的转化过程,但该区段烟气再循环低氮效果有限,最大降幅9%。再循环烟气可以替代部分一次风,以维持足够的风室风压,进而降低穿过煤层气流的O2浓度,从而强化链条炉区段燃烧特性的低氮特征,实现链条炉的NO_x减排。随着工业锅炉NO_x排放指标的不断提高,烟气再循环作为一项有效的前置低氮环节,能有效降低整个低氮系统的投资,进而取得较好的经济性。     

中小型燃气锅炉NO_x源头控制及低氮燃烧技术研究进展

介绍了燃气燃烧过程中热力型NO_x和快速型NO_x的生成机理,从对空气的预处理、对燃气和空气的混合分配两个方面综述了燃烧源头控制降低NO_x排放的技术,主要包括高温空气燃烧、柔和燃烧、浓淡燃烧、分级分段燃烧、脉动燃烧、烟气再循环等单一技术和旋流与富氧燃烧、烟气再循环与高温空气燃烧等组合技术;结合低NO_x原理,综述了低NO_x技术的实现形式,指出低NO_x燃烧技术的发展前景。     

生物质与煤混合富氧燃烧过程中NO和N_2O的排放特性研究

为了研究燃烧气氛、进口氧气浓度、生物质掺混比、燃烧温度以及过量氧气系数对循环流化床(CFB)富氧燃烧过程中NO,N_2O排放特性以及燃料中N的转化特性的影响,以棉秆和大同烟煤为燃料,在50 k W循环流化床燃烧试验台上进行了空气气氛和O_2/CO_2气氛下的生物质与煤混合燃烧试验。试验结果表明:与空气气氛相比,O2/CO2气氛下,NO,N_2O的排放量和燃料中N的转化率均降低;随着进口氧气浓度和燃烧温度的升高,NO的排放量均升高,N_2O的排放量和燃料中N的转化率均降低;随着生物质掺混比的增大,NO的排放量和燃料中N的转化率降低,N_2O的排放量升高;NO,N_2O的排放量以及燃料中N的转化率均随过量氧气系数增大而升高。     

分解炉内贫氧高CO2燃烧条件下挥发分NO生成机理

基于GRI3.0详细动力学反应机理数据库,采用生成速率分析方法,从化学反应动力学角度分析水泥分解炉内煤粉挥发分贫氧燃烧时低温、高浓度CO2条件下挥发分NO生成机理及挥发分中HCN转化生成NO的主要转化路径.分析结果表明,煤粉在过量空气系数为0.8的贫氧燃烧条件下,分解炉内高浓度CO2气氛会促进NO生成,增大NO的排放浓度;850～950℃温度范围内,CO2体积分数为0%～35%条件下挥发分NO生成的主要机理反应式为N+O2(→)NO+O、HNO+H(→)H2+NO和N+CO2(→)NO+CO;高体积分数CO2通过推进反应FINO+H(→)H2+NO和N+CO2(→)NO+CO促进NO生成;其中HNO是NO生成过程中最重要的活性含氮中间产物,对NO生成起主要的贡献作用;HCN氧化生成NO的主要反应路径为HCN先转化生成NHi,再进一步转化生成HNO活性含氮中间体,最终生成NO.     

吡咯类氮富氧燃烧的分子动力学研究

采用基于ReaxFF反应力场的分子动力学模拟方法研究了不同燃烧温度和氧浓度条件下吡咯在O_2/CO_2和O_2/N_2气氛下燃烧的反应速率和自由基、中间产物及最终产物的分子数变化规律,从微观上探索吡咯在O_2/CO_2气氛下的燃烧机理。研究表明:吡咯富氧燃烧的主要产物包括HCN、NO、N_2、CO_2、CO和H_2O等,主要的中间体和自由基包括C_4H_4N、NCO、HNCO、C_4H_4ON、CHO_2、CN、H、OH、O和HO_2等;随着燃烧温度的升高,O_2/CO_2和O_2/N_2气氛下NO的生成量都随之增加;随着氧气浓度的升高,更多的HCN、NCO、HNCO及其它含氮中间产物转化为NOx,从而使其生成量增加;在燃料与氧气的化学当量比Φ=0.5和1时,O_2/CO_2气氛中NO的生成量比O_2/N_2气氛中的NO的生成量高,在Φ=2时两种气氛中生成的NO量相当。     

燃料稀释对富氧空气_甲烷扩散火焰中氮氧化物生成的影响

本研究的目的是揭示富氧燃烧过程中的氮氧化物生成机理,针对富氧火焰特性探讨NOx抑制机制机理。文中以对向流扩散火焰为对象,利用详细的基元反应动力学模型研究了燃料稀释对富氧空气／甲烷扩散火焰中氮氧化物生成的影响,稀释剂为N2或CO2。结果表明,随着燃料中稀释组分浓度的变化,火焰结构和NO生成的决定机理显著变化;同时发现,随稀释剂CO2浓度增大,NO的排放指数EINO(Emission Index of NO)单调减少,随稀释刺N2稀释时EINO存在最大值。     

富氧燃烧条件下锅炉燃料燃烧计算研究

以常规锅炉燃料燃烧计算方法为基础,对富氧燃烧锅炉的燃料燃烧计算方法展开研究。通过将富氧锅炉与常规锅炉的热力系统进行比较,建立了进行富氧锅炉燃料燃烧计算的基本模型。在此基础上首先提出了富氧燃烧条件下燃料所需理论助燃剂量和理论烟气量的计算方法,随后进行了考虑烟气再循环和不考虑烟气再循环2种条件下的实际烟气量的分析计算,其中包括各种烟气成分的体积量的计算,最后根据富氧燃烧锅炉热力系统的特点,推导出了富氧燃烧条件下烟气质量、烟气密度、飞灰质量浓度和烟气焓的计算公式。对富氧燃烧条件下锅炉的燃料燃烧计算进行了详细分析,为今后发展和完善富氧锅炉热力计算方法提供必要的理论基础。     

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.     

Electrodeposition of CuInSe2 and CuInS2 films

Various methods to electrodeposit films of CuInSe(S)₂ are discussed. Two basically different methods are treated separately: electrodeposition of the ternary CuInSe(S) systems and deposition of a CuIn alloy followed by annealing in an Se(S)-containing atmosphere.Electrodeposition of the ternary CuInSe(S) systems includes CuInS₂ (and CuIn₅S₈) plated from a thiourea bath. Morphological, compositional and photoelectrochemical behaviour of these layers is discussed. Attempts to plate CuInSe₂ from an SeO₂-containing bath and CuInS₂ from a non-aqueous sulphur-containing bath are also treated.Discussion of the second method, deposition of a CuIn alloy, concentrates on the alloy deposition step. Both co-deposition of copper and indium and sequential deposition of indium on copper are treated, with emphasis on the morphology of the layers.     

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.     

Photocatalytic reduction of CO2 with H2O on CuO/TiO2 catalysts

Carbon dioxide was photocatalytically reduced to produce methanol and ethanol in the presence of CuO-loaded titania powders suspended in water containing Na₂SO₃ as the hole scavenger. The photocatalysts were synthesized by an impregnation method using P25 (Degussa) as support. At the optimum amount of copper oxide loading (3 wt%), the methanol and ethanol yields were 12.5 and 27.1 μmol/g-catal., respectively, following 6 h of UV illumination. The redistribution of photogenerated charge carriers in CuO/TiO₂ facilitates electron trapping and prohibits the recombination of electrons and holes, which significantly increases photoefficiency. The addition of Na₂SO₃ promotes the formation of ethanol.