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In this study, the characteristics of hydrogen flame stabilization in porous medium combustor were investigated. The flame was observed in a quartz tube. The porous medium was oxide-bonded silicon carbide (OB-SiC) or aluminum oxide (Al 2 O 3 ) with 60 PPI and 30 PPI pore size distributions. The results indicated that under a low equivalence operation, the flame would transform from surface combustion to interior combustion with an increased heating value. Under a high equivalence ratio, both interior combustion and flashback transition existed at the same time. The thermal conductivity of silicon carbide is higher than that of aluminum oxide. Thus, interior combustion region was more extensive under a low equivalence ratio operation with a high premixed gas velocity. Flashback was apparent for Al 2 O 3 under high an equivalence ratio with low a premixed gas velocity. Consequently, hydrogen flame stability could be controlled by the pore size distribution and thermal conductivity of the porous media, input heating value and input equivalence ratio. [ABSTRACT FROM AUTHOR]

Abstract: A porous medium-catalyst hybrid reformer for CO2 conversion by dry auto-thermal reforming (DATR) was investigated in this study, and its operating range was discovered. The hybrid design was used to enhance the oxidative heat release by internal heat recirculation during exothermic reaction conditions, thereby increasing the CO2 conversion efficiency. The experimental results show that the CO2 conversion could be enhanced with higher catalyst inlet temperatures. The examination of the operating range of DATR showed that the CO2 conversion efficiency increased at higher reaction temperatures and CO2/CH4 ratios (≧1). Moreover, DATR in high temperature conditions must be carried out with high O2/CH4 ratios. Under these conditions of high oxygen content, CO2 generation and reduction reactions occur simultaneously. Overall, optimal CO2 conversion can be obtained with an O2/CO2 ratio of approximately 0.5. At these conditions, CO2 conversion efficiency can reach approximately 13% without external heat addition. [Copyright &y& Elsevier]

Abstract: A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H2-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO2/CH4 and O2/CH4 ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O2/CH4 = 0.7–0.9 and CO2/CH4 = 0.0–2.0). [Copyright &y& Elsevier]

This paper investigated the design of a porous medium–catalyst hybrid reformer for CO 2 conversion by dry auto-thermal reforming, with emphasis on the reaction temperature distribution. In the reforming process, the reaction under excess enthalpy was explored by interface temperature measurement and infrared thermograph observation in a porous medium assisted packed-bed catalyst reactor. The hybrid design was arranged with the catalytic packed-bed in the downstream of the porous medium. In the arrangement, the reactants were preheated by internal heat recirculation and the conversion of CO 2 was enhanced by the catalyst surface reaction. The temperature measurement at the axial position and infrared thermograph observation on the catalyst packed-bed indicated that the peak temperature could be stabilized and held at the interface of the PM and catalyst bed, which significantly improved the propagation and stability of the flame. This was helpful to the improvement of both thermal wave transfer and internal heat recirculation. [ABSTRACT FROM AUTHOR]