An experimental investigation of stability and operation of a biogas fueled porous burner

Porous media combustion constitutes a particularly attractive technology, allowing operation in ultra-lean combustion regimes with excellent fuel interchangeability and low levels of pollutant emissions. This work presents a comprehensive experimental characterization of a state-of-the-art porous burner fuelled with a simulated biogas mixture, in terms of thermal efficiency and pollutant emissions. The combustor is a rectangular two-layer porous burner with an Al2O3 flame trap and a 10 ppi (pores per inch) SiSiC foam. The burner was operated with a mixture of 60% methane and 40% carbon dioxide. An extensive stability mapping was performed in order to establish the range of operation in terms of thermal loads and mixture equivalence ratios. Gas and solid phase temperature profiles were measured using thermocouples and infrared thermography respectively, and gaseous emissions were quantified using an online gas analyser sampling system and a gas chromatographer. The results revealed wide stability with respect to thermal loads, low NOx and CO levels, and negligible hydrocarbon emissions. The effects of CO2 addition on burner operation and efficiency, the relative impact of thermal load on temperature and emission values with respect to equivalence ratio were investigated. The comparably strong physical effect of the CO2 addition was discussed against its chemical impact on the processes.