Experimental Study On Catalytic Combustion Characteristics Of Methane On Metal Foam Monoliths

Ignition and stable combustion in confined space is the key technology which matters the application and development of micro- or small- scale combustor. The low-temperature catalytic combustion is an important way to solve this problem. This project focuses on the research of metal foam monolithic catalysts and catalytic combustion characteristics for methane-air in small-scale combustor.The Fe-Ni alloy metal(70%Fe-30%Ni) foams were used as the catalyst support.And the metal foam based monolithic catalysts(Pd/Al2O3/Fe-Ni) were prepared by wet impregnation. Then the methane catalytic oxidation characteristics over metal foam monolithic catalyst in a small-reactor were experimentally studied. The influences of reactor temperature, CH4 concentration and mixture flow rate on methane conversion rate were analyzed. The results showed that conversion rate increased with the increase of reactor temperature, CH4 concentration and the decrease of mixture flow rate. Especially, the temperature was the key factor for CH4 conversion. In addition, the effects of hydrogen addition on methane catalytic oxidation were investigated. The results showed that the adding of hydrogen didn't promote the catalytic oxidation of methane. However, the methane conversion rate declined with it. And the methane conversion rate significantly decreased with the increase of equivalence ratio.The effects of the coating load of Al2O3 sol, the content of active component, and the modification of Ce and Zr on the performance of metal foam based monolithic catalysts were experimentally studied. The Al2O3 sol loading had an optimum value of12~20%; the content of active component(Pd) should not be more than 1.3% of catalyst mass; Ce0.25 Zr0.75 O2 were the most optimum addition.The methane catalytic combustion characteristics were studied in micro-scale tube combustor with the foam metal substrate catalyst(Pd/Al2O3/Fe-Ni). The results showed that the ignition start-up stage can be divided into three stages: the temperature soared to the highest temperature; the temperature fell slowly from thehighest point; the temperature in the burner tended to be stable, which reached the steady combustion state. Premixed gas velocity had a great influence on the flame and the distribution of temperature in the burner. The higher the velocity was, the brighter the flame was, and also the higher temperature in the burner. However, the effect of equivalent ratio on temperature was very small; the temperature in the burner is slightly reduced with the decrease of the equivalent ratio. Finally, the exhaust were tested by GC which found that: the combustion efficiency reached the maximum(99.9%); the selectivity of CO2 in the exhaust rose with the decrease of the equivalent ratio, but the selectivity of CO reduced with the decrease of the equivalent ratio.When equivalent ratio is close to or equal to 1.0, the reaction of water gas shift(WGS)yields H2 under the action of the catalyst.