Investigation of the hydrogen-enriched methane combustion in a domestic boiler with porous burner on emissions and performance

Hydrogen is considered one of the most promising renewable fuel alternatives for decarbonizing the gas sector. The transition from fossil fuels to carbon-free alternatives is essential for achieving full carbon neutrality. Rather than a direct shift from natural gas systems to pure hydrogen, a gradual integration of hydrogen into the existing natural gas supply offers a more feasible transition pathway. In this study, the effects of utilizing a 20 % hydrogen-enriched methane mixture in a condensing boiler with a porous burner, commonly used for heating in residential and commercial applications, were investigated. Emission values for NOx, O2, CO2, and CO were obtained from experimental studies conducted at two different fan speeds. The experimental results revealed that the condensing boiler, originally designed to operate on 100 % methane, exhibited an approximate 5 % reduction in thermal power when operated with a fuel mixture of 20 % hydrogen and 80 % methane. Notably, a reduction in flue gas emissions was observed. At maximum thermal power, CO2 concentrations in the flue gas decreased from 9.3 % to 8.3 %, CO levels dropped from 71 ppm to 42 ppm, and NOx emissions reduced from 19 mg/kWh to 12 mg/kWh. Additionally, three-dimensional CFD simulations were conducted by using the AramcoMech 2.0 mechanism, which includes 25 species and 105 reactions, to further analyze the boiler's performance. A numerical comparison was conducted between the 100 % methane and the 20 % hydrogen-enriched methane fuel inputs. The porous burner was modeled using a porous media approach within the numerical framework. The numerical results were validated against experimental data, confirming the reliability of the simulations. These findings underscore the potential of hydrogen-enriched methane as a viable and environmentally friendly alternative fuel for condensing boilers equipped with porous burners.