Self-aspirating/air-preheating porous medium gas burner

Abstract

This study proposes a novel design of an atmospheric gas burner that introduces the concept of heat recirculation combustion by means of porous media combustion technology. A combustor and heat recirculation unit, used for preheating the combustion air, are part of the assembly of the porous material. The combustor is a self-aspirating annular porous medium burner (APMB) formed by a packed bed of alumina spheres with a diameter of 10 mm. A porous radiant recirculation heater was integrated into the APMB to obtain an elevated air temperature. To stabilize flames at the middle of the porous media packed bed, the flow velocity of the mixture has to be equal to the flame propagation velocity, making this a critical criterion for the design of the burner. A critical variable required to determine the flame velocity is the primary equivalence ratio. It was predicted using the empirical formula derived from the experimental data, and considers the momentum equation and pressure drop in the porous medium burner. Operation of the burner with firing rates from 21 to 44 kW resulted in evaluated air temperatures of 136–252 °C, yielding maximal temperatures greater than the adiabatic flame temperature. The NOx emissions were low because of the combustion within a porous medium. The CO emissions were high compared with the conventional burner but still conformed to the requirements of the national standard.