Digital colour image processing based measurement of premixed CH4 + air and C2H4 + air flame chemiluminescence

The experimental investigation of flame properties based on digital colour analysis has been conducted. In particular, the practicality of obtaining physical flame chemiluminescence characteristics through the inherent colour-filtering architecture employed in the digitisation of flame images was demonstrated. This is important as radical emission signals is an effective non-intrusive tool for deriving a number of useful combustion properties. In this study, a processing procedure was introduced which allows commercial digital colour camera to be transformed into a semi-quantitative device for radiation-based combustion diagnostics. Results have shown that the digitised primary colour outputs can be abstractly related to various emanating radicals in premixed CH₄ + air and C₂H₄ + air flames. Both the RGB and HSV colour models were applied and each was found to be effective in tackling different issues in the overall make-up of the colour processing scheme. HSV-based numerical identity was able to recognise the appropriate RGB signal related to the radical chemiluminescence-induced digital colouration. From the recognised flame colour regime, the validity of the observed B and G signal correlation to emission characteristics of CH1 and ${\text{C}}_2^1$ radiation was conclusive by comparing with the results from the well-established spectrometry and optically filtered imaging methods. The abstract colour signals depicted similar radical chemiluminescence behaviour variations along with changes in equivalence ratio, reactant composition, and the increase of heat-release in the reactant flow.     

Experimental and numerical study of CH4/CH3Cl/O2/N2 premixed flames under oxygen enrichment

A comprehensive experimental and numerical study has been conducted to understand the influence of CH₃Cl addition on CH₄/O₂/N₂ premixed flames under oxygen enrichment. The laminar flame speeds of CH₄/CH₃Cl/O₂/N₂ premixed flames at room temperature and atmospheric pressure are experimentally measured using the Bunsen nozzle flame technique with a variation in the amount of CH₃Cl in the fuel, equivalence ratio of the unburned mixture, and level of oxygen enrichment. The concentrations of major species and NO in the final combustion products are also measured. In order to analyze the flame structure, a detailed chemical kinetic mechanism is employed, the adopted scheme involving 89 gas-phase species and 1017 elementary forward reaction steps. The flame speeds predicted by this mechanism are found to be in good agreement with those deduced from experiments. Chlorine atoms available from methyl chloride inhibit the oxygen-enhanced flames, resulting in lower flame speeds. This effect is more pronounced in rich flames than in lean flames. Although the molar amount of CH₃Cl in the methane flame is increased, the temperature at the post flame is not significantly affected, based on the numerical analysis. However, the measured concentration of NO is reduced by about 35% for the flame burning the same amount of methyl chloride and methane at the oxygen enrichment of 0.3. This effect is due to the reduction of the concentration of free radicals related to NO production within the flame. In the numerical simulation, as CH₃Cl addition is increased, the heat flux is largely decreased for the oxygen-enhanced flame. It appears that the rate of the OH + H₂ → H + H₂O reaction is reduced because of the reduction of OH concentration. However, the function of CH₃Cl as an inhibitor on hydrocarbon flames is weakened as the level of oxygen enrichment is increased from 0.21 to 0.5. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 103–111, November–December, 2006.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 Over Sr-Promoted La2O3

The influence of CO₂ and H₂O on the activity of 4% Sr-La₂O₃ mimics that observed with pure La₂O₃, and a reversible inhibition of the rate is observed. CO₂ causes a greater effect, with decreases in rate of about 65% with O₂ present and 90% in its absence, while with H₂O in the feed, the rate decreased around 35-40% with O₂ present or absent. The influence of these two reaction products on kinetic behavior can be described by assuming competitive adsorption on the surface, incorporating adsorbed CO₂ and H₂O in the site balance, and using rate expressions previously proposed for this reaction over Sr-promoted La₂O₃. In the absence of O₂, the rate expression is $$r_{N_2 } = \frac{{k'P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }},$$ which yields a good fit to the experimental data and gives optimized equilibrium adsorption constants that demonstrate thermodynamic consistency. With O₂ in the feed, nondifferential changes in reactant concentrations through the reactor bed were accounted for by assuming integral reactor behavior and simultaneously considering both CH₄ combustion and CH₄ reduction of NO, which provided the following rate law for total CH₄ disappearance: $$(r_{{\text{CH}}_{\text{4}} } )_{\text{T}} = \frac{{k'_{{\text{com}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} + k'_{{\text{NO}}} P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }}.$$ The second term of this expression represents N₂ formation, and it again fit the experimental data well. The fitting constants in the denominator, which correspond to equilibrium adsorption constants, were not only thermodynamically consistent but also provided entropies and enthalpies of adsorption that were similar to values obtained with other La₂O₃-based catalysts. Apparent activation energies typically ranged from 23 to 28 kcal/mol with O₂ absent and 31-36 kcal/mol with O₂ in the feed. With CO₂ in the feed, but no O₂, the activation energy for the formation of a methyl group via interaction of CH₄ with adsorbed NO was determined to be 35 kcal/mol.     

CH4/CO2混合气置换强化含氮低品质甲烷的浓缩

针对CO₂置换吸附分离CH₄/N₂过程中CO₂再生困难的问题,采用少量产品气CH₄真空吹扫以提高CO₂的解吸效果,并以解吸得到的CH₄/CO₂混合气为置换步骤的置换气,通过置换来强化含氮低品质甲烷的浓缩过程。以自制椰壳活性炭为吸附剂,对CH₄/CO₂混合气置换强化吸附回收含氮低品质甲烷工艺过程进行了实验与模拟研究。在gPROMS软件中建立并求解固定床吸附分离模型方程,预测了CH₄、N₂ 和CO₂在自制椰壳活性炭上的竞争吸附穿透曲线,通过预测结果和实验的对比,验证了数学模型方程的准确性。对比了不同置换气强化吸附分离低品质甲烷的效果,结果表明CH₄/CO₂混合气置换强化相对于CO₂置换强化可获得更高纯度产品。进行了CH₄/CO₂混合气置换强化真空变压吸附循环实验,可以将14%的CH₄/N₂和53%的CH₄/CO₂联合富集到98.8%,同时获得77.8%的回收率。     

Intensification of low-grade methane enrichment in nitrogen mixture by CH4/CO2 displacement

To solve the problem of CO₂ uncompleted desorption in the process of CO₂ displacement enhancing the adsorption separation of CH₄/N₂, a small amount of product gas CH₄ was used as purge gas to improve the CO₂ desorption. CH₄/CO₂ mixture gas obtained from desorption step was recycled as the displacement gas to enhance the enrichment of low-grade methane in nitrogen mixture. In this work, the research conducted the experiments for CH₄/N₂ separation using CH₄/CO₂ displacement intensification adsorption and the laboratory-made coconut shell activated carbon as sorbent. The mathematical models were built in gPROMS and the accuracy of models was verified by comparison of simulations and CH₄/N₂/CO₂ breakthrough experiments. The performance of enrichment of low-grade methane with displacement intensification using different displacer was compared. The result showed that the process with CH₄/CO₂ displacement had higher purity product than CO₂ displacement. The CH₄/ CO₂ mixed gas replacement enhanced vacuum pressure swing adsorption cycle experiment was carried out, which can jointly enrich 14% CH₄/ N₂ and 53% CH₄/CO₂ to 98.8%, and at the same time obtain a recovery rate of 77.8%.     

Investigation of the Phase Equilibria of CO2/CH3OH/H2O and CO2/CH3OH/H2O/H2 Mixtures

The storage of excess electricity from renewable energy sources is nowadays a crucial topic. One promising technology is the methanol (CH₃OH) synthesis from H₂/CO₂ mixtures. The achievable one‐pass conversion is limited within this exothermic equilibrium reaction. A possibility to overcome this limitation would be withdrawing CH₃OH and H₂O from the gas phase through in situ condensation under reaction conditions. In this work, the phase equilibrium for mixtures representative for different degrees of conversion was studied. A view cell was employed to determine systematically the single‐ and two‐phase regimes and obtain phase envelopes for mixtures of H₂, CO₂, CH₃OH, and H₂O from 66 to 305 °C and 61 to 233 bar. Furthermore, the densities in the single‐phase area were determined and quantified by an empirical model.     

Evolution of hot corrosion resistance of YSZ,Gd2Zr2O7, and Gd2Zr2O7 + YSZ composite thermal barrier coatings in Na2SO4 + V2O5 at 1050 °C

This paper compares the hot corrosion performance of yttria stabilized zirconia (YSZ), Gd₂Zr₂O₇, and YSZ + Gd₂Zr₂O₇ composite coatings in the presence of molten mixture of Na₂SO₄ + V₂O₅ at 1050 °C. These YSZ and rare earth zirconate coatings were prepared by atmospheric plasma spray (APS). Chemical interaction is found to be the major corrosive mechanism for the deterioration of these coatings. Characterizations using X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that in the case of YSZ, the reaction between NaVO₃ and Y₂O₃ produces YVO₄ and leads to the transformation of tetragonal ZrO₂ to monoclinic ZrO₂. For the Gd₂Zr₂O₇ + YSZ composite coating, by the formation of GdVO₄, the amount of YVO₄ formed on the YSZ + Gd₂Zr₂O₇ composite coating is significantly reduced. Molten salt also reacts with Gd₂Zr₂O₇ to form GdVO₄. Under a temperature of 1050 °C, Gd₂Zr₂O₇ based coatings are more stable, both thermally and chemically, than YSZ, and exhibit a better hot corrosion resistance.     

Adsorption of H2, CO2, CH4, CO,N2 and H2O in Activated Carbon and Zeolite for Hydrogen Production

Abstract

The design of a layered pressure swing adsorption unit to treat a specified off-gas stream is based on the properties of the adsorbent materials. In this work we provide adsorption equilibrium and kinetics of the pure gases in a SMR off-gas: H₂O, CO₂, CH₄, CO, N₂, and H₂ on two different adsorbents: activated carbon and zeolite. Data were measured gravimetrically at 303–343 K and 0–7 bar. Water adsorption was only measured in the activated carbon at 303 K and kinetics was evaluated by measuring a breakthrough curve with high relative humidity.     

O2/CO2气氛中水蒸气预混CH4燃烧特性与烟气余热梯级利用方案

对O2/CO2气氛中甲烷预混水蒸气燃烧特性及主要污染物生成进行了数值模拟研究,在加湿燃烧的基础上提出一种全新的清洁燃烧方式,即在保证甲烷流量一定时,通过改变入口处水蒸气的质量分数,研究水蒸气预混比Rf(0, 0.1, 0.2, 0.3, 0.4和0.5)对燃烧流场、燃烧组分和污染物浓度的影响。结果表明,随Rf增大,燃烧反应速率上升、燃烧效率提高且污染物排放量降低。模拟所得甲烷预混水蒸气的最优气氛为81%CH4/19%H2O,提出了一种高效节能的O2/CO2气氛下水蒸气预混CH4燃烧与烟气余热梯级利用方案。     

The reaction of CO2 with CH4 to synthesize H2 and CO over nickel-loaded Y-zeolites

Nickel metal introduced into Y-zeolite exhibited a high catalytic activity in the dehydro-genation of methane and in the hydrogenation of carbon dioxide with methane to obtain hydrogen and CO at about 850 K. The activity strongly depended on the nickel amount in NaY, and the catalytic properties were influenced by the kind of cations in the Y-zeolite. The higher CO₂ conversion was obtained over Ni supported on non-acidic zeolites.     

H2,CO,N2,O2和CH4在碳膜中的扩散

Diffusion of pure H2,CO,N2,O2and CH4 gases through nanoporous carbon membrane is investigated by carrying out non-equilibrium molecular dynamics(NEMD)simulations.The flux,transport diflusivity and acti-vation energy for the pure gases diffusing through carbon membranes with various pore widths were investigated.The simulation results reveal that transport diffusivity increases with temperature and pore width.and its values port diflusivities are comparablc With that of Rao and Sircar(J.Membr.Sci.,1996).indicating the NEMD simula-tion method iS a good toO]for predicting the transport diflusivities for gases in porous materialS.which iS always difficult to be accurately measured by experiments.     

交流和直流电场对天然气贫燃火焰的影响

对常温、常压下定容燃烧弹中的甲烷/空气预混贫燃火焰的传播和燃烧特性进行了研究,对比了相同电压有效值下15 kHz高频交流电压和直流电压对火焰的影响。结果表明：两种电压加载方式下,火焰形状均发生变形,当过量空气系数一定时,交流电场作用下的火焰在水平方向上的拉伸比直流电场下的剧烈,且混合气越稀,两者差异越明显;与未加载电压相比,当过量空气系数为1.2、1.4和1.6时,交流电场作用下的平均火焰传播速度分别提高49.14%、76.54%、117.65%,直流电场下分别提高41.38%、58.02%、62.75%,交流电场下压力峰值增幅分别为9.48%、11.48%、14.20%,直流电场下增幅分别为4.46%、5.25%、8.76%。因此,相同电压有效值下,15 kHz高频交流电场对火焰的促进作用较直流电场更明显。     

交流和直流电场对天然气贫燃火焰的影响

对常温、常压下定容燃烧弹中的甲烷/空气预混贫燃火焰的传播和燃烧特性进行了研究, 对比了相同电压有效值下15 kHz高频交流电压和直流电压对火焰的影响。结果表明:两种电压加载方式下, 火焰形状均发生变形, 当过量空气系数一定时, 交流电场作用下的火焰在水平方向上的拉伸比直流电场下的剧烈, 且混合气越稀, 两者差异越明显;与未加载电压相比, 当过量空气系数为1.2、1.4和1.6时, 交流电场作用下的平均火焰传播速度分别提高49.14%、76.54%、117.65%, 直流电场下分别提高41.38%、58.02%、62.75%, 交流电场下压力峰值增幅分别为9.48%、11.48%、14.20%, 直流电场下增幅分别为4.46%、5.25%、8.76%。因此, 相同电压有效值下, 15 kHz高频交流电场对火焰的促进作用较直流电场更明显。     

NO + H2 reaction on Pd/Al2O3 under lean conditions: kinetic study

This paper deals with the kinetics of the NO + H₂ + O₂ reactions on Pd/γ-Al₂O₃. Steady state rate measurements have been discussed in the light of previous mechanism proposals involving a dissociation step of molecular NO adsorbed species on Pd. In the absence of oxygen, the dissociation of NO_ads species is assisted by chemisorbed H atoms. However, different kinetic features have been observed in the presence of oxygen. Practically, the light-off curve of NO shifts towards higher temperature in the presence of O₂. In addition the H₂ + O₂ reaction extensively occurs in the temperature range of this study. Such tendencies have been explained by changes in the adsorptive properties of noble metals and also in the nature of elementary steps for the dissociation of NO. In the presence of a large extent of O₂, hydrogen coverage would sharply drop and would not further assist the dissociation of NO as in the absence of O₂.     

Equilibrium analysis of CH4, CO,CO2, H2O,H2, C mixtures in C–H–O atom space using Gibbs free energy global minimization

Gibbs free energy minimization is employed to carry out thermodynamic equilibrium analysis studies of mixtures containing methane, carbon monoxide, carbon dioxide, water, and hydrogen ideal gases, and possibly solid carbon. The employed global minimization approach represents a general, unifying, conceptual framework that allows reaction and phase equilibrium analysis to be simultaneously carried out in the atom-mol fraction space (a_H, a_O) , thus capturing in a comprehensive manner the equilibrium behavior of a number of industrially important processes, such as methane reforming (steam, dry, energetically enhanced), and methanation. Two theorems are presented, establishing necessary and sufficient (necessary) feasibility and regularity (optimality) conditions for the aforementioned minimization problem. The equilibrium results obtained through application of these theorems are guaranteed to be globally optimal. They quantify in (a_H, a_O) space, the feasible region, the carbon formation region, and all species mole over total atom-mol normalized ratios, for a range of temperatures and pressures.     

CH4掺混H2的燃烧数值模拟及掺混比合理性分析

本工作针对天然气掺氢燃烧技术在燃气锅炉的最佳掺混比开展数值模拟研究,以小火焰燃烧器为研究对象,计算了在空气氛围、恒定过氧系数、不同甲烷掺混氢气比条件下,掺氢比对燃料燃烧温度、燃烧速率、主要污染物排放浓度的影响.其中燃烧机理采用GRI-MECH 3.0简化机理,该反应包含24个基元反应,涉及17种组分.计算结果表明,随掺...     

Adsorption and temperature programmed desorption of NO,NO + O2, NO2 and NO + NO2 over CoH-ZSM-5

The NO₂, NO (O₂) adsorption and temperature programmed desorption (TPD) were studied systematically to probe into the selective catalytic reduction of NO by methane (CH₄–SCR) over CoH-ZSM-5 (SiO₂/Al₂O₃ = 25, Co/Al = 0.132–0.312). Adsorption conditions significantly affect the adsorption of NO, NO₂ and NO + O₂. Adsorbed NO species are unstable and desorbed below the reactive temperature 523 K. Increasing adsorption temperature results in the decrease of the adsorbed NO species amount. The amount of –NO_y species formed from NO₂ adsorption increases with the increase of NO₂ concentration in the adsorption process, while decreases significantly with the increase of adsorption temperature. Though NO species are adsorbed weakly on CoH-ZSM-5, competitive adsorption between NO and –NO_y species decreases the amount of adsorbed –NO_y species. Similar desorption profiles of NO₂ were obtained over CoH-ZSM-5 while they were contacted with NO₂ or NO + O₂ followed by TPD. If NO₂ was essential to form adsorbed –NO_y species, the amount of adsorbed –NO_y species for NO + O₂ adsorption should be the least among the adsorptions of NO₂, NO + O₂ and NO + NO₂ because of the lowest NO₂ concentration and highest NO concentration. In fact, the amount of adsorbed –NO_y species is between the other two adsorption processes. These indicate that the formation of adsorbed –NO_y species may not originate from NO₂.