Experimental investigation of a radiant porous burner performance with simulated natural gas, biogas and synthesis gas fuel blends

Abstract

The general performance of a porous inert media burner system in terms of radiative efficiency, fuel flexibility, pollutant formation and reliability was determined experimentally. The porous burner of choice has been previously proven of being capable to operate on conventional and alternative gaseous fuels. The present study examines its operation with virtual blends of model fuels in order to assign and evaluate synergistic effects. In this regard, the present work examines mixtures of CH4, CO, H2 and CO2 on a two-layer burner with a 10 ppi (pores per inch) SiSiC foam flame zone. The study focused on gaseous and solid phase temperature levels and pollutant formation trends over various nominal thermal loads in the lean combustion regime. The burner optimum operating range was identified and results revealed low NOx levels. For a given stoichiometry, the burner is characterized by a NOx level threshold systematically below 20 ppm, independently of the fuel, with however, distinct behaviour especially with respect to CO2 content. The opposing effects of CO and H2 addition on CH4/air combustion, aside the influence of CO2 dilution, were assessed on burner operation and radiation efficiency. The CO2 addition increased measured CO emission levels and decreased the radiation efficiency of the burner. This may also be attributed to the lower adiabatic flame temperature and burning velocity of CO2 enriched blends, as also acknowledged by supportive numerical calculations. The relative impact of thermal load on temperature, emissions and burner radiation efficiency with respect to equivalence ratio was also studied. It was identified that the specific burner design, delivers wide power flexibility at lean combustion regimes, providing, at the same time, low total pollutant emissions, i.e. less than 50 ppm and high radiation efficiency, i.e. up to 70% for low thermal loads and depending on the stoichiometry.