Methane combustion over low-emission catalytic foam burners

Abstract

Fully pre-mixed porous burners, in which methane combustion takes place close to the burner surface are stimulating an increasing interest since they allow lower flame temperatures and NO x emissions, due to rapid heat removal, thanks to either radiative or convective transfer mechanisms. The present investigation enlightens the further advantages obtainable via the deposition of suitable catalysts onto a porous burner. An industrial ceramic foam support was considered for this purpose: two foam supports were deposited with the LaMnO 3-perovskite catalyst, according to two different techniques both based on in situ pyrolysis. For one support (the surface-catalysed burner) the catalyst was deposited, as a thin layer (about 1 mm deep); onto the outlet burner surface (burner-deck), the region where most of the combustion is expected to take place. For the other one (the fully-catalysed burner), the catalyst was deposited within the entire foam matrix. The two catalytic burners and a reference non-catalytic one were comparatively tested in a pilot plant (maximum power of about 30 kW, corresponding to about 1600 kW/m 2). All three burners showed excellent NO x (<70 ppmv for excesses of air >20%) and HC emissions (<10 ppmv). Conversely, the CO produced at low superficial power (<300 kW/m 2) and excess air (<10%) values was much higher for the non-catalysed burner than for the catalytic ones. Furthermore, the catalyst entailed another positive effect: at the lowest superficial power (190 kW/m 2) it stabilised the combustion towards lower excesses of air, to the benefit of higher thermal efficiency.