Jingyu Ran

Low-concentration methane combustion over a Cu/γ-Al2O3 catalyst: effects of water

The influence of water on low-concentration methane oxidation over a Cu/γ-Al2O3 catalyst was investigated in a fixed bed reactor. This paper studied the effect of water on the activity of methane combustion, using parameters such as water reversible adsorption, regeneration of the activity and surface characteristics of the catalyst. Apparent activation energy was found by experiments, and water surface coverage was calculated using the Langmuir equation. It was found that the activity of methane combustion over a Cu/γ-Al2O3 catalyst decreased with time due to water adsorption. The inhibitory effect generated by water weakened as the temperature rose above 550 °C. Reactivity could be refreshed if the catalyst particles were scavenged by N2. Kinetic experiments showed that, if water was added into the feed, apparent activation energy (Ea) increased noticeably (81.4 kJ mol−1 → 153.0 kJ mol−1) and the reaction order with respect to water was −0.6 to −1. Using the Langmuir equation, it could be concluded that the coverage of water adsorption on catalytic active sites increased noticeably as vapor was introduced into the feed. If the temperature increased, water coverage went down and tended towards 0% above 625 °C.

Investigation on the effect of water vapor on the catalytic combustion of methane on platinum

ABSTRACT The effect of H2O on the catalytic combustion of CH4 on Pt was investigated experimentally and numerically. The ignition temperature obtained by measuring the exit temperature of the H2O/CH4/Air mixtures flow through Pt coated honeycomb channels showed that the ignition temperature was related to the CH4 and H2O mole fraction. The numerical results showed that the adsorption of H2O blocked CH4 oxidation, leading to the increase of the ignition temperature and the reforming reaction did not occur with C/O ratio less than 0.43. However, with C/O ratio increasing, H2O could produce catalytic reforming reaction with CH4, and H2 produced in the reaction could increase the conversion of CH4. This study is helpful to provide some useful information for the design of the micro-combustor.

Planar Laser-Induced Fluorescence Research on Flame Quenching and OH Radical Behavior Near the Walls

AbstractThis paper details a quantitative joint Reynolds number, equivalence ratio, wall material, and quenching distance imaging experiment designed to investigate OH radical behavior near the wal...

Kinetic consequences of methane combustion on Pd, Pt and Pd–Pt catalysts

The kinetic consequences of methane combustion on PdxPt1−x oxide surfaces are investigated with kinetic data and density functional theory treatments. The catalytic activity of monometallic palladium drops significantly with time, and this loss is larger at higher temperatures. However, the addition of platinum to palladium catalysts significantly improves their stability. Besides, the Pd-rich bimetallic catalysts show higher activity for methane conversion. Turnover rates are independent of O2 pressure (>10 kPa) but depend linearly on CH4 pressure for all the catalysts. The calculated C–H bond activation energies are almost identical for Pd1.0, Pd0.75Pt0.25 and Pd0.5Pt0.5. However, the Pt-rich catalysts (Pd0.25Pt0.75) show poor activity, and their activation energies and pre-exponential factors increase with increase in the platinum content of the catalyst. In these catalysts, methane dissociation is the only kinetically relevant step, but it occurs on different active sites. H2O and CO2 (>3–5 kPa) strongly inhibit methane combustion by titrating surface vacancies in a quasi-equilibrated adsorption–desorption step for Pd-containing catalysts. The DFT-derived C–H bond activation energies for O-saturated Pt surfaces are much larger than the values for PdO(101) surfaces, which is in agreement with the experimental results. Models of Pd–Pt oxide surfaces were built on the basis of XRD results and known structures of oxide Pd and Pt monometallic catalysts. Although the atom arrangement of the PdO(101)/Pt(100) outermost layer is similar to that of PdO(101), the C–H bond activation energy for PdO(101)/Pt(100) is much larger than that of PdO(101) because the surface Pd atoms on PdO(101)/Pt(100) are highly coordinated. However, when the Pd content is high enough (>25 mol%) in the Pd–Pt bimetallic catalysts, the low PdO(101) activation energy (61 kJ mol−1) is retrieved for two monolayers of PdO(101) on Pt(100) (67 kJ mol−1).

Auto-adaptive Air Distribution and Structure Optimization of Ejector Burner for Biomass Alcohol Fuels

A plenty of studies on the utilization of biomass alcohol fuels have been conducted, but combustion efficiency and stability of this fuels still need to be improved. Based on biomass alcohol fuels (bio-methanol and bio-ethanol), this paper studied auto-adaptive air distribution characteristics and optimum structure parameters of an ejector burner by numerical simulation method. Also, an experiment was conducted to verify the numerical results. The results show that the mole air entrainment ratio (MAER) keeps almost constant when the ejector fuel nozzle exit locates at the segment between the ejector throat and the suction chamber entrance, but a bigger ratio α would lead to a higher MAER till the α is bigger than 8.5 for bio-methanol and 11.5 for bio-ethanol. The bio-ethanol fuel is more beneficial for air carrying role because of its big molecular weight. Operation pressure (Pw) has a little impact on MAER of the two fuels, but the rise of back pressure (Pb) would lead to rapid decrease of MAER for the two fuels. For the optimum structure burners, the MAER can be maintained at the value of theoretical complete combustion. Its changing rate is less than 2.3% for bio-methanol and 2.5% for bio-ethanol when the burner load changes from 30% to 120%, which is highly consistent with the experimental results. The optimum burner can distribute air supply automatically with the changing of burner load.

Influence of the Structure of Micro Premixing Chamber on the Uniformity of Flow Distribution and Premixing Characteristics

In micro combustors, the residence time of gas is dramatically reduced. It is much more important to improve combustion efficiency and stability of the micro-combustor by improving the uniformity of flow distribution and mixed results in micro premixing chamber. The flow distribution in micro premixing chamber is analyzed. The influence of micro premixing chamber structures (including the diameter of fuel inlet, numbers of arc-shaped and straight micro-channels, distance and numbers of subordinate fuel inlets) on the uniformity of flow distribution and premixing characteristics is numerical investigated. The influence of the different structure of micro premixing chamber is gained. It is an important guide for designing high efficient micro premixing devices.Copyright

3-D Simulation of Rotary Atomized Nozzle Flow Characteristics at Low Pressure

In order to realize liquid (oil etc.) atomized and to improve the combustion efficiency, the atomization or adding moisture is required by atomized nozzle in the oil burner and some power driven thrusters. Based on physics model and some suitable hypothesizes, the 3-D mathematical models for rotary atomized nozzle with micro-expanded tangent channel at low pressure are presented, and the same time, the various simulation tests are taken with the k-{epsilon}/RNG models and SIMPLE method, the tests results shown: The angle({theta}) of the micro-expanded tangent channel plays an important role for the fluid characteristics, if {theta} 0, the solid cone in nozzle are formed easily, but its energy loss is bigger. While the initial pressure p{sub 0}=0.3 Mpa, U{sub x,0}=0, U{sub y,0}=0, U{sub z,0}=-0.2 m/s, the circum-fluence at the exit of the nozzle is not exactly formed with {theta}=5.8 and the energy loss is reduced and the atomized angle can get 80 deg.. The nozzle can be widely adequate to the medium atomized instrument about the oil burner and some power driven thrusters. (authors)