Research on hydrogen-blended combustion, emission and operation characteristics of gas boilers

Hydrogen-blended combustion of gas boilers is an important way to reduce carbon emissions in urban heating, but there are few studies on the hydrogen-blended combustion, emission and operation characteristics of gas boilers. This paper analyses the influence of the hydrogen blending ratio on various operation parameters of gas boilers, and discusses the changes in physical parameters, combustion and emission characteristics of the hydrogen-blended natural gas, and boiler operation optimization strategies. The results show that the hydrogen-blended natural gas can significantly reduce CO2emissions, but the significant changes in its physical parameters require re-adjustment of combustion parameters to maintain boiler efficiency. Increasing the hydrogen blending ratio will accelerate the laminar flame propagation speed, expand the flammability limit, and increase the flame temperature, leading to increased thermal NOxemissions (especially when the temperature is higher than 1 600 K). Adjusting the excess air coefficient can suppress NOxgeneration, but its effectiveness diminishes at high hydrogen blending ratios (large than 50%). Current research primarily focuses on small household boilers (25-28 kW), confirming that hydrogen blending can improve condensation efficiency and energy-saving potential. However, the data on high hydrogen blending ratios in large-capacity industrial boilers remain scarce.