OP-II-3

OP-III-B-10CATALYTIC OXIDATION OF LEAN BIOGAS-AIRShahamiri S.A., Wierzba I.Department of Mechanical and Manufacturing Engineering, Schulich School ofEngineering, University of Calgary, Alberta, Canada, iwierzba@ucalgary.caLow heating value gaseous fuel mixtures, such as those derived from theprocessing of biosources and landfill gases have a common feature of being madeup of primarily methane with relatively large concentrations of the diluents carbondioxide with some nitrogen. However, it is widely known that the presence of suchdiluents with the methane will seriously impede its oxidation mainly due to the lowfuel concentration and the very low associated resulting temperatures [1,2]. Thesuccessful combustion of these gases needed to permit their effective exploitation incommon combustion devices and processes requires further research anddevelopment. The catalytic oxidation of homogeneous fuel-air mixtures containinglow concentrations of fuel may represent a potentially effective approach for theirefficient and clean combustion [3,4,5]. In the present work the catalytic oxidation oflean homogeneous mixtures of CH 4 -CO 2 and air in a Pt/Al 2 O 3 packed bed reactorwas modeled using detailed surface and gas reaction chemical kinetics. The model isbased on two-phase treatment approach and accounts for the effects of the transportprocesses between the two phases on the reaction rates. It was applied to simulatea non-adiabatic lab scale reactor fed with preheated homogeneously premixed fueland air and operating at atmospheric pressure [6]. The results were obtained for inletfeed temperatures of 600 - 900 K and equivalence ratios of 0.15 - 0.55 withconcentration of CO 2 in the fuel ranging from 0 to 90%. It was shown that for theseequivalence ratio values the presence of CO 2 did not hinder the oxidation ratesmarkedly until the fuel contained more than ~70% of carbon dioxide, when theoxidation rate became affected significantly. As it can be seen (Fig 1) this isespecially pronounced with the higher equivalence ratio feed. Moreover, the effectsof using higher values of equivalence ratio had a greater positive effect on theoxidation of methane than its impeding by equivalent increases in the concentrationof CO 2 in the fuel. It is also shown that for an equivalence ratio of 0.15, the energyreleased by the reaction appears insufficient to provide the preheating required overthe feed mixture temperatures considered (Fig 2). For the feed equivalence ratio of0.35 the heat released is greater than required for preheating when T inlet > ~700 Kand concentration of CO 2 in the fuel is less that 60%. For the higher 0.55 equivalenceratio case the positive heat balance is observed for almost all the cases considered.198