Combustion Of Low-concentration Methane Research Articles

Effects of Key Influencing Factors on the Flame Inclination of Low Concentration Methane (LCM) Combustion in Porous Burner

ABSTRACT In present work, a local thermal non-equilibrium numerical model of low concentration methane combustion in porous media is established. The modified thermal effective thermal conductivity of foam ceramics was introduced. The heat and mass dispersion effect as well as the influence of porous media structure on the heat transfer were fully considered. Studies found that the combustion flame front of low concentration methane in porous media always show a S-shaped state under special conditions. The influencing factors of inlet velocity, methane concentration, wall heat loss, and the porous burner size were analyzed. Results show that without initial thermal perturbation and the absence of defects in the porous media, the flame front in porous burner still has the possibility of inclination. As the inclination of the flame front continues to increase, the flame keeps approaching the burner outlet until blow off. Among the considered four influencing factors, the size of porous burner has the greatest influence on the inclination of flame front. As the burner diameter increases from 0.04 m to 0.12 m, the inclination angle of the flame front increases continuously, and the maximum inclination angle is 36°. The flame inclination will cause uneven temperature distribution downstream of the burner and local heat concentration. With the increase of wall heat loss, the high-temperature zone downstream of the burner will evolve into a local high-temperature zone near the flame front. With the reducing of porous burner diameter, the inclinational instability could be suppressed to some extent.

High performance for oxidation of low-concentration methane using ultra-low Pd in silicalite-1 zeolite

Abstract 0.123%Pd encapsulated in nanosized silicalite-1 (MFI) zeolite catalysts has been prepared by direct hydrothermal conditions, and its catalytic performance at the low concentration methane combustion was studied. The temperatures for methane ignition (T10%), the half-conversion temperature (T50%) and the total conversion temperature (T90%) over Pd/S-1-in (in-situ method) catalyst are 261, 329 and 382 °C, respectively, which are lower than the corresponding temperatures of Pd/S-1-im (incipient impregnation method) catalyst. Moreover, the properties are further enhanced by introducing CeO2 into the Pd/S-1-in catalyst. The conversion rate decreased slightly from 91 to 85% when the reaction is carried out at 450 °C for 100 h at the gas hourly space velocities (GHSV) of 112500 mL g−1 h−1. The XPS analysis showed that Pd clusters were encapsulated within the porous rather than on the surface of the crystal by in-situ method. The HRTEM studies demonstrated that the Pd particle encapsulated within Silicalite-1 zeolites are well dispersed and evenly distributed throughout the Silicalite-1 zeolites. The average size of in situ Pd particle encapsulated in Silicalite-1 zeolite is 1.7 nm, which is much smaller than the impregnated Pd/S-1-im catalyst (2.8 nm).

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.

Catalytic Combustion of Low Concentration Methane over Catalysts Prepared from Co/Mg-Mn Layered Double Hydroxides

A series of Co/Mg-Mn mixed oxides were synthesized through thermal decomposition of layered double hydroxides (LDHs) precursors. The resulted catalysts were then subjected for catalytic combustion of methane. Experimental results revealed that the Co4.5Mg1.5Mn2LDO catalyst possessed the best performance with theT90=485°C. After being analyzed via XRD, BET-BJH, SEM, H2-TPR, and XPS techniques, it was observed that the addition of cobalt had significantly improved the redox ability of the catalysts whilst certain amount of magnesium was essential to guarantee the catalytic activity. The presence of Mg was helpful to enhance the oxygen mobility and, meanwhile, improved the dispersion of Co and Mn oxides, preventing the surface area loss after calcination.

Research on Catalytic Combustion of Low Concentration Methane in Combustion Channel of Compact Reformer

The combustion channel of compact methane reformer includes fuel flow duct, porous layer and solid connector. There are heat transport and multi-component species diffusion/convection processes in porous structure. The transfer processes are coupled with methane catalytic combustion, and affect the performance and stability of reformer. A 3D in-house code has been developed to simulate the mass and heat transfer processes involving chemical reactions in the reformer channel in specific condition (mass fraction of CH4YCH4is less than 1% in the mixture of methane and air). It shows that, catalytic combustion reactions mainly tack place on the porous layer near inlet with a higher temperature area, the biggest heat flux region from the bottom wall is found near the higher temperature area. The reaction rate of methane, temperature of porous layer and heat flux increase with the increase of YCH4. In general, 0.4% is an adequate value for YCH4. The research has a benefit meaning to provide a guideline for the improvement and design for compact methane reformer.