Nonpremixed Catalytic Combustion of Methane in a Fluidized Bed Reactor

The present work addresses the performance of a catalytic fluidized bed combustor characterized by non-premixed feedings of methane and air, relevant to the combustion of mixtures within the flammability limits. This extension is of increasing interest with reference to practical applications of gas fluidized bed boilers when considering the high potentiality required and the safety problems related to a flammable feeding. The catalytic combustion of methane has been investigated in a 0.10 m bubbling fluidized bed reactor. Copper dispersed on porous ç-Al2O3 spheres (1 mm diameter) characterized by high mechanical strength has been used as catalyst. The effect of design variables such as methane inlet concentration, bed temperature, and superficial gas velocity on methane conversion has been quantified in the ranges 4-10 vol %, 650-750 °C, and 0.40-1.30 m/s, respectively. The propensity to attrition of the catalyst has been separately investigated under the experimental conditions tested. Conversion of methane was complete at temperatures ranging from 650 to 750 C depending on the operative conditions in the reactor (inlet fuel concentration and fluidization velocity). As a consequence, under the conditions investigated, a maximum thermal power of about 4.5 kW could be produced by the reactor with fuel emissions lower than 100 ppm and without any formation of CO or NOx. Results have been interpreted in the light of a simple reactor model which assumes a plug-flow pattern for the gas through the bed and mth-order catalytic kinetics with respect to fuel concentration.