| With the rapid development of micro-electro-mechanical system (MENS), theminiature power system has been widely used in many respects. Especially it has a goodapplication prospect in microelectronics, information, biology, medical, aerospace,national defense and so on. The investigation of miniature power system has become ahot research topic in the academia. The micro-burner which has been made lots ofresearch by domestic and foreign experts is the significant component of miniaturepower system. At present, ordinary lithium battery is the most widely power deviceapplied in the miniature power system, the energy density of the best lithium battery isjust0.50MJ/kg in the world, however, the energy density of micro-burner used methanecan reach to about45MJ/kg, even if the energy conversion efficiency is only10%, themicro-burner can provide the energy density that is also about10times of commonlithium battery, so the miniature burner has wide application prospect. Nevertheless theincreasing of surfacevolume ratio of combustion chamber leads to serious heat lossbecause of the tremendous shrink of the combustion chamber of micro-burner, and atthe same time the combustion is instable and easy to flame-out in micro-cavity, theseare the difficulties of developing micro-combustor. A lot of studies show that the mix ofa little of hydrogen in methane can improve the combustion characteristics inmicro-cavity. Therefore, it becomes a feasible way that autothermal reforming reactionof methane (ATR) is applied to methane burning in micro-cavity. The research to thecharacteristics of autothermal reforming reaction of methane (ATR) in micro-cavity canset a stage for the application and development of micro-combustor.In this paper, a series of basic research of the characteristics of autothermalreforming reaction of methane (ATR) in micro-reactor are investigated, by using theCFD software of computational fluid dynamics, the effect of catalytic walltemperature, inlet velocity of feed gas, water-carbon ratio (W/C), oxygen-carbon ratio(O/C), operating pressure, Ni base catalyst activeness density on the methaneconversion, product yield, and catalytic wall carbon deposition and outlet componentand so on. In this paper, the straight circular micro-reactor and the cyclonemulti-cylinder micro-reactor are respectively taken for research object studing thecharacteristics of autothermal reforming reaction of methane (ATR), and then the tworesults are compared. Studies have shown that the rise of temperature leads to the increase of diffusioncoefficient (D). The reactants are easier adsorbed on the catalyst and the resultants areeasier desorbed from the catalyst, which will greatly promote methane auto thermalreforming reactions to occur. But in high temperature environment, the presence of lotsof CO2and H2will promote water gas shift reaction in the opposite direction (water gasshift reaction is exothermic), then part of the CO2and H2convert to CO and H2O. Forsubtle straight pipe reactor, it is appropriate that the catalytic wall temperature does notexceed1123K. For the mini-cyclone multi-layer drum reactor, the catalytic walltemperature should not exceed1000K. To obtain the same methane conversion rate andthe yield, the catalytic wall temperature of the straight circular micro-reactor is higherthan it of the cyclone multi-cylinder micro-reactor150K or so. This is because the latterhas small heat loss and it is more energy-efficient.In the straight circular micro-reactor, the increase of water-carbon ratio (W/C) canimprove the conversation of methane, when the water-carbon ratio (W/C) exceeds2.2,the appropriate excessive water can promote the occurrence of water gas shift (WGS)reaction, and increase product yield of hydrogen, and at the same time can inhibit theformation of carbon deposition. In the cyclone multi-cylinder micro-reactor, the bestwater-carbon ratio (W/C) of autothermal reforming reaction of methane (ATR) is2.1,this result coincides with the result of the study in the straight circular micro-reactor.From the simulation for two reactors can conclude that the methane conversionrate increases with the raise of oxygen-carbon ratio (O/C), however, whenoxygen-carbon ratio (O/C) excees0.3, oxygen appear excessive, which can lead to theyield of hydrogen and carbon monoxide decreasing, and at this time the carbondeposition on catalytic wall also drop rapidly. The studies shows that high methaneconversion rate, high hydrogen and carbon monoxide yield and low carbon depositionof catalytic wall can also be got when oxygen-carbon ratio (O/C) is0.4. The increase ofNi base catalyst activeness density can improve methane conversion rate and hydrogen,carbon monoxide yield, nevertheless from the comprehensive analysis of catalyticreaction effect and catalyst cost, the optimal Ni base catalyst activeness density is9.98×10-6kmol/m2.Increasing the inlet velocity will cause the stay time of reactant gas, thereby reducethe methane conversion rate as well as hydrogen, carbon monoxide yield in themicro-cavity. But it can effectively reduce the total carbon deposition on the catalyticwall. So choosing a reasonable entrance velocity of the feed gas is essentially important for the micro-electro-mechanical system (MEMS), powered by the micro-reactor ofmethane catalytic auto-thermal reforming (ATR) reaction.The pressure loss of the cyclone multi-cylinder micro-reactor is20-30times biggerthan the straight circular micro-reactor, therefore the operating pressure performs lessaffection on the reforming reaction in the micro-straight channel reactor than in thehelical multi-layer cylindrical reactor. Raising the operating pressure can improve thedriving force of the gas transport in the flow field, the actual amount of gas that diffuseto the catalyst active site and contribute to the reforming reaction, and increase theprobability of reaction occurrence. On the other hand, considering the bearing capacityand cost requirements of the instrument, the operating pressure should not evaluateblindly. |
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