In this paper, the combustion characteristics of biogas in a Porous Radiant Burner (PRBBG) designed for domestic cooking appliances are presented. Developed PRBBG consists of two layers of porous matrices viz., Silicon Carbide (SiC) and Alumina (Al2O3) and operates in the biogas flow range of 177 to 530 l/h with stable equivalence ratio (ϕ) range of 0.75 to 0.95. The effects of biogas flow rate and equivalence ratio on thermal efficiency (ηth) and emission characteristics of the burner are investigated and also compared with its conventional counterpart. Overall performance assessment shows that PRBBG operating at lower equivalence ratio and lower firing power has better thermal efficiency with lower CO and NOx emissions. The performance of the burner in terms of temperature mapping suggests that firing power variation is of higher importance than that of equivalence ratio. The maximum temperature difference between the center and the periphery of the burner surface is found to be ~ 83 °C at an equivalence ratio of 0.95. The thermal efficiency varies in the range of 51-62% and its maximum is at 0.75 equivalence ratio and 177 l/h flow rate of biogas. Within the range of studied biogas flow rate range, CO emission is in the range of 29-80 ppm and NOx concentration was lower than 4 ppm. Whereas, for Conventional Burner (CB), thermal efficiency, CO, and NOx emission are found in the range of 43-52%, 211-276 ppm, and 9-15 ppm, respectively. The overall performance showed that PRBBG is capable of burning a lean biogas-air mixture with better thermal efficiency and lower emissions.
Keywords: Biogas; CO and NOx emissions; Porous Media Combustion; Porous Radiant Burner; Thermal efficiency.