Adiabatic burning velocity of H2–O2 mixtures diluted with CO2/N2/Ar

Global warming due to CO₂ emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO₂, N₂, and Ar) on the laminar burning velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar burning velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO₂, N₂, and Ar as diluents. Measured burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar burning velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H₂/O₂/CO₂ flames with 65% CO₂ dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H₂/O₂/CO₂ cellular flame structure and cell count from computed flame matched well with the experimental cellular flame.     

Combustion,performance and emissions of a diesel engine with H2, CH4 and H2–CH4 addition

Experiments were conducted to investigate the combustion and emission characteristics of a diesel engine with addition of hydrogen or methane for dual-fuel operation, and mixtures of hydrogen–methane for tri-fuel operation. The in-cylinder pressure and heat release rate change slightly at low to medium loads but increase dramatically at high load owing to the high combustion temperature and high quantity of pilot diesel fuel which contribute to better combustion of the gaseous fuels. The performance of the engine with tri-fuel operation at 30% load improves with the increase of hydrogen fraction in methane and is always higher than that with dual-fuel operations. Compared with ULSD–CH₄ operation, hydrogen addition in methane contributes to a reduction of CO/CO₂/HC emissions without penalty on NO_x emission. Dual-fuel and tri-fuel operations suppress particle emission to the similar extent. All the gaseous fuels reduce the geometry mean diameter and total number concentration of diesel particulate. Tri-fuel operation with 30% hydrogen addition in methane is observed to be the best fuel in reducing particulate and NO_x emissions at 70 and 90% loads.     

Revision of the NaBO2–H2O phase diagram for optimized yield in the H2 generation through NaBH4 hydrolysis

The binary phase diagram NaBO₂–H₂O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH₄ hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO₂·4H₂O (Na[B(OH)₄]·2H₂O), NaBO₂·2H₂O (Na[B(OH)₄]), NaBO₂·2/3H₂O (Na₃[B₃O₄(OH)₄]), NaBO₂·1/3H₂O (Na₃[B₃O₅(OH)₂]) and NaBO₂ (Na₃[B₃O₆]), and their thermal stabilities have been studied. The boundaries of the different Liquid + Solid equilibria for the temperature range from −10 to 80 °C have been determined, confirming literature data at low temperature (20–50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO₂·4H₂O, occurring at −7 °C, has been determined by DSC. The Liquid–Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO₂·2/3H₂O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH₄ hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO₂–H₂O binary phase diagrams and its consequence related to hydrogen storage through NaBH₄ hydrolysis.     

Effects of alumina powder characteristics on H2 and H2O2 production yields in γ-radiolysis of water and 0.4 M H2SO4 aqueous solution

The effects of powder characteristics on H₂ and H₂O₂ productions in ⁶⁰Co γ-radiolysis were studied in pure water and in 0.4 M H₂SO₄ aqueous solutions containing alumina powders. In 0.4 M H₂SO₄ solution, the H₂ yields strongly depended on alumina structures and decreased in the order of α > θ > γ-alumina, although the specific surface areas increased as α < θ < γ. The yields increased with increasing specific surface area when compared among α-alumina. In pure water, similar dependence was observed but not as strong as that for 0.4 M H₂SO₄ solution. The H₂O₂ yields were strongly decreased by adding the alumina powders in both water and 0.4 M H₂SO₄ aqueous solution, although the amounts of decrease were almost neither correlated with specific surface areas nor structures. The enhancing H₂ production was discussed in terms of the electron supply from alumina to aqueous solution as well as the adsorption of OH radicals on alumina surfaces.     

Start-up behaviors of a H2SO4–H2O distillation column for the 50 NL H2/H sulfur–iodine cycle

The sulfur–iodine (SI) cycle to produce hydrogen from water requires a multistage distillation column to concentrate a sulfuric acid solution. To design a concentration process of a sulfuric acid solution that can be applied to the cycle, its static and dynamic simulation is essentially demanded. A 50 NL H₂/h scale SI test facility to be operated under a pressurized environment has been constructed in Korea. This study focuses on the sulfuric acid multi-stage distillation column (SAMDC-50L) for the 50 NL H₂/h SI test facility. The SAMDC-50L was designed and installed in 2012. Based on the design specifications and operation method, a start-up behavior of the SAMDC-50L has been analyzed using the simulation code “KAERI-DySCo”. As a result of the start-up dynamic simulation, it is confirmed that the SAMDC-50L will approach to the steady state value within 30,000 s to fulfill the hydrogen production rate of 50 NL H₂/h. On the other hand, it is expected that the operation time approaching a steady state decreases with an increase in the set point of the condenser temperature until a dew point of the top vapor product and the time required for the transition to the complete steady state is increased with an increasing reflux ratio and reboiler hold-up.     

A comparison of the emission and impingement heat transfer of LPG–H2 and CH4–H2 premixed flames

Experiments were performed to add hydrogen to liquefied petroleum gas (LPG) and methane (CH₄) to compare the emission and impingement heat transfer behaviors of the resultant LPG–H₂–air and CH₄–H₂–air flames. Results show that as the mole fraction of hydrogen in the fuel mixture was increased from 0% to 50% at equivalence ratio of 1 and Reynolds number of 1500 for both flames, there is an increase in the laminar burning speed, flame temperature and NO_x emission as well as a decrease in the CO emission. Also, as a result of the hydrogen addition and increased flame temperature, impingement heat transfer is enhanced. Comparison shows a more significant change in the laminar burning speed, temperature and CO/NO_x emissions in the CH₄ flames, indicating a stronger effect of hydrogen addition on a lighter hydrocarbon fuel. Comparison also shows that the CH₄ flame at α = 0% has even better heat transfer than the LPG flame at α = 50%, because the longer CH₄ flame configures a wider wall jet layer, which significantly increases the integrated heat transfer rate.     

O2/CO2/H2O气氛下CO燃烧机理的分子动力学模拟研究

采用反应分子动力学(ReaxFF MD)模拟方法研究了O₂/CO₂/H₂O气氛下CO的燃烧。结果表明：根据化学平衡原理,高浓度CO₂抑制CO的氧化,同时CO₂在高温下参与反应CO₂+H—→CO+OH,进一步抑制CO氧化。在较低温度条件下,较高浓度H₂O的三体效应显著,抑制了CO氧化。另一方面,在较高温度条件下,H₂O参与的H₂O+H—→H₂+OH和H₂O+O—→OH+OH反应占据其化学作用的主导地位,进而促进CO氧化。随着O₂浓度的增加,CO的氧化速度加快。     

Laminar burning velocities and flame characteristics of CO–H2–CO2–O2 mixtures

Laminar burning velocities of CO–H₂–CO₂–O₂ flames were measured by using the outwardly spherical propagating flame method. The effect of large fraction of hydrogen and CO₂ on flame radiation, chemical reaction, and intrinsic flame instability were investigated. Results show that the laminar burning velocities of CO–H₂–CO₂–O₂ mixtures increase with the increase of hydrogen fraction and decrease with the increase of CO₂ fraction. The effect of hydrogen fraction on laminar burning velocity is weakened with the increase of CO₂ fraction. The Davis et al. syngas mechanism can be used to calculate the syngas oxyfuel combustion at low hydrogen and CO₂ fraction but needs to be revised and validated by additional experimental data for the high hydrogen and CO₂ fraction. The radiation of syngas oxyfuel flame is much stronger than that of syngas–air and hydrocarbons–air flame due to the existence of large amount of CO₂ in the flame. The CO₂ acts as an inhibitor in the reaction process of syngas oxyfuel combustion due to the competition of the reactions of H + O₂ = O + OH, CO + OH = CO₂ + H and H + O₂(+M) = HO₂(+M) on H radical. Flame cellular structure is promoted with the increase of hydrogen fraction and is suppressed with the increase of CO₂ fraction due to the combination effect of hydrodynamic and thermal-diffusive instability.     

A numerical study on the effects of H2 addition in non-premixed turbulent combustion of C3H8–H2–N2 mixture using a steady flamelet approach

This study has been implemented in two sections. At first, the turbulent jet flame of DLR-B is simulated by combining the k–ε turbulence model and a steady flamelet approach. The DLR-B flame under consideration has been experimentally investigated by Meier et al. who obtained velocity and scalar statistics. The fuel jet composition is 33.2% H₂, 22.1% CH₄ and 44.7% N₂ by volume. The jet exit velocity is 63.2 m/s resulting in a Reynolds number of 22,800. Our focus in the first part is to validate the developed numerical code. Comparison with experiments showed good agreement for temperature and species distribution. At the second part, we exchanged methane with propane in the fuel composition whilst maintaining all other operating conditions unchanged. We investigated the effect of hydrogen concentration on C₃H₈–H₂–N₂ mixtures so that propane mole fraction extent is fixed. The hydrogen volume concentration rose from 33.2% up to 73.2%. The achieved consequences revealed that hydrogen addition produces elongated flame with increased levels of radiative heat flux and CO pollutant emission. The latter behavior might be due to quenching of CO oxidation process in the light of excessive cold air downstream of reaction zone.     

H2O2作添加剂对SNCR脱硝工艺的影响

为了改善选择性非催化还原(SNCR)脱硝工艺的反应特性,以H2O2为添加剂,对SNCR过程进行了实验研究。在小型SNCR实验台上进行实验,以N2作为载气,以纯NO模拟NOx气氛,初始NO浓度为360μL/L,O2=4%,H2O=8%,NSR=1.5。通过对实验结果进行分析,得到H2O2对低温下的脱硝率有促进作用,对最大脱硝率以及最佳脱硝温度没有影响,最大脱硝率依然为80%左右,最佳脱硝温度为925℃。另外还分析了H2O2对NH3浓度、HNCO浓度、NO2浓度、N2O浓度以及N2转化率的影响及其原因。     

HI extraction by H3PO4 in the Sulfur–Iodine thermochemical water splitting cycle: Composition optimization of the HI/H2O/H3PO4/I2 biphasic quaternary system

Iodine excess separation from hydriodic acid (HI) is one of the most challenging steps of the Sulfur–Iodine thermochemical water splitting cycle. One promising method is the extraction of HI by using phosphoric acid (H₃PO₄), with the subsequent separation of gaseous hydriodic acid from water and H₃PO₄ by a distillation step.     

Effect of N2/CO2 dilution on laminar burning velocity of H2–air mixtures at high temperatures

The laminar burning velocities of H₂–air mixtures diluted with N₂ or CO₂ gas at high temperatures were obtained from planar flames observed in externally heated diverging channels. Experiments were conducted for an equivalence ratio range of 0.8–1.3 and temperature range of 350–600 K with various dilution rates. In addition, computational predictions for burning velocities and their comparison with experimental results and detailed flame structures have been presented. Sensitivity analysis was carried out to identify important reactions and their contribution to the laminar burning velocity. The computational predictions are in reasonably good agreement with the present experimental data (especially for N₂ dilution case). The burning velocity maxima was observed for slightly rich mixtures and this maxima was found to shift to higher equivalence ratios (Ф) with a decrease in the dilution. The effect of CO₂ dilution was more profound than N₂ dilution in reducing the burning velocity of mixtures at higher temperatures.     

Preferential oxidation of CO in H2 stream on Au/ZnO–TiO2 catalysts

A series of gold catalysts supported on ZnO–TiO₂ with various ZnO contents were prepared. ZnO–TiO₂ was prepared by incipient-wetness impregnation using aqueous solution of Zn(NO₃)₂ onto TiO₂. Gold catalysts with nominal gold loading of 1 wt. % were prepared by deposition-precipitation (DP) method. Various preparation parameters, such as pH value and Zn/Ti ratio on the characteristics of the catalysts were investigated. The catalysts were characterized by inductively-coupled plasma–mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The preferential oxidation of CO in H₂ stream (PROX) on these catalysts was carried out in a fixed bed micro-reactor with a feed of CO: O₂: H₂: He = 1: 1: 49: 49 (volume ratios) and a space velocity of 30,000 ml/g h. Limited amount of oxygen was used in the feed. A high gold dispersion and narrow gold particle size distribution was obtained. Au/ZnO–TiO₂ with Zn/Ti atomic ratio of 5/95 showed the highest CO conversion at room temperature. The conversion increased with increasing temperature even in the presence of limited amount of oxygen, showing suppression in H₂ oxidation. Au/ZnO–TiO₂ prepared at pH 6 had a higher CO conversion and higher selectivity of CO oxidation than those prepared at other pH values. The addition of ZnO on TiO₂ resulted in higher dispersion of gold particles and narrow particle size distribution. The stronger the Au–Zn(OH)₂ interaction, the finer the supported Au nanoparticles, and the better the catalytic performance of the catalyst for PROX reaction. Part of Au was in Au⁺ state due to the interaction with Zn(OH)₂ and nano Au size. The oxidation state of gold species played an important role in determining its CO conversion and selectivity of CO oxidation in hydrogen stream. The catalysts were stable at 80 °C for more than 80 h.     

Effect of RuO2–CoS2 anode nanostructured on performance of H2S electrolytic splitting system

An innovative, nanostructured composite, anode electrocatalyst, material has been developed for the electrolytic splitting of (100%) H₂S feed content gas operating at 135 kPa and 150 °C. A new class of anode electrocatalyst with general composition, RuO₂–CoS₂ has shown great stability and desired properties at typical operating conditions. This configuration showed stable electrochemical operation over the period of 24 h and also exhibited a maximum current density of (0.019 A/cm²). The kinetic behaviors of various anode-based electrocatalysts demonstrated that, exchange current density, which is a direct measure of the electrochemical reaction, increased with RuO₂–CoS₂-based anodes. Moreover, high levels of feed utilization were possible using these materials. Electrochemical performance, current density, and sulfur tolerance were enhanced compared to the other tested anode configurations. The structural, microstructural and surface behavior of RuO₂–CoS₂ anode electrocatalyst was investigated in detail.     

缺陷态Bi2MoO6光热催化CO2和H2O还原成CO的性能

在不同温度下采用乙二醇溶剂热合成法合成Bi₂MoO₆催化剂(BMO-x,x=140、160、180),BMO-160在450℃下煅烧的样品为BMO。用XRD、BET、SEM、EDS、UV-visDRS、XPS、in-situ DRIFTS等表征方法研究其理化特性,建立BMO和BMO-x(x=140、160、180)催化剂的反应性能与孔道结构、材料形貌和缺陷空位的构效关系。结果表明,适宜的溶剂合成温度可以形成更高的孔隙率,调控氧空位的占比,有助于产生更好的催化性能。其中,BMO-160的CO产率更高,这是由于在160℃溶剂热合成温度下制备的样品形貌更优,氧空位占比适中。     

木质素磺酸盐在微波/H2O2体系中降解行为研究

通过比较处理前后紫外可见光谱、红外吸收光谱、凝胶过滤色谱(GPC)的变化和对降解产物的气质分析,研究了木质素磺酸钠在微波/H2O2体系中的降解行为。试验发现,微波/H2O2体系能有效促使木质素降解,降解过程中苯丙烷侧链和苯环都遭到了不同程度的破坏。在低浓度双氧水条件下,中间产物中含有大量芳香醛;在高浓度双氧水条件下,芳香醛含量减少,低分子量脂肪酸含量增多。降解后残渣的分子量减小,分布变窄。通过对木质素磺酸钠降解后的产物分析,推测了其在微波/H2O2体系中降解的可能机理,为木质素资源的高效综合利用寻找新的途径。     

H2 and CO production over a stable Ni–MgO–Ce0.8Zr0.2O2 catalyst from CO2 reforming of CH4

Ni–Ce_0.8Zr_0.2O₂ and Ni–MgO–Ce_0.8Zr_0.2O₂ catalysts were investigated for H₂ production from CO₂ reforming of CH₄ reaction at a very high gas hourly space velocity of 480,000 h⁻¹. Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited higher catalytic activity and stability (CH₄ conversion >95% at 800 °C for 200 h). The outstanding catalytic performance is mainly due to the basic nature of MgO and an intimate interaction between Ni and MgO.     

Aliphatic–aromatic polyimide blends for H2 separation

In this work the synthesis of a semi aliphatic BTDA-DAH polyimide and their blends with BTDA-ODA and BTDA-DDS polyimides was carried out in order to improve the H₂ permselective properties of polyimides. The syntheses were made using the well-known two steps method and the silylation method. The prepared films were characterized by FTIR, DSC, thermal stability and fluorescence spectroscopy. Intercatenary distances (d-spacing) and gas separation properties were also investigated. PI blend membranes presented only one glass transition temperature (Tg) intermediate between those of the neat polyimides. Fluorescence spectra were a useful tool to recognize electron-donor and electron-acceptor interactions indicating intermolecular charge-transfer complex (CTC) formation which were confirmed by UV–Vis absorptions. As a result, a decrease in the intercatenary distances and a shift for both IR and fluorescence bands of polyimide blends were measured. PI blend membranes showed a permeability decrease with respect to the neat ones, while the selectivity increased according to X-ray diffraction results. To analyze the polyimide blend permselectivities, H₂/CH₄, H₂/CO₂, H₂/O₂ and H₂/N₂ systems were chosen. As a result, H₂/CH₄ separation factor of PI blends was among the highest reported by other authors using traditional membrane materials.     

In situ thermal desorption of H2 from LiNH2–2LiH monitored by environmental SEM

This article describes in situ heating and observation of a LiNH₂–2LiH mixture in an environmental scanning electron microscope (ESEM). The LiNH₂–2LiH mixture showed extensive morphological changes with heating and attendant hydrogen desorption. Static images and real-time movies were obtained during the dehydrogenation process. H₂ evolution commences at ∼150 °C (LiNH₂ + 2LiH → Li₂NH + H₂ + LiH), and continues until ∼410 °C. Dramatic morphological changes are observed at 220 and 410 °C (Li₂NH + LiH → Li₃N + H₂). The material converts to a microcrystalline phase at higher temperatures (>500 °C). The observed H₂ desorption and morphological changes occur at temperatures in good agreement with those measured by complementary analytical methods. This is the first time the major structural and morphological changes attendant on H₂ loss from this system have been observed in situ and in real time.