An assessment of the operating conditions of the micromix combustion principle for low NOx industrial hydrogen burners: Numerical and experimental approach

In the present study, a multi-nozzle hydrogen burner based on the micromix combustion principle (MCP) and designed to operate under atmospheric pressure and without preheated air was investigated both numerically and experimentally. Previous investigations regarding this type of burner have shown low NOx x emissions and no risk of flashback, which are the two main issues when burning pure hydrogen. Numerical models were calculated based on a CFD code, and the burner performance was assessed under various operating conditions, including thermal powers between 5 and 25 kW and excess air ratio between 1.3 and 2. The importance of turbulence-chemistry interaction modelling and differential diffusion effects, particularly for highly diffusive flames such as hydrogen, has been widely addressed. All numerical results were validated with experimental results from a laboratory-scale burner using thermocouple measurements, including the corresponding radiative corrections. An infrared camera was used to detect and study the flame shape under various operating conditions. The turn-down of the multi-nozzle hydrogen burner was extensively analysed, focusing on the penetration depth or, equivalently, the momentum flux ratio as a highly sensitive design parameter. Low Reynolds number flames were also considered, demonstrating a collapse of the MPC under these conditions. These conclusions emphasize the relevance of this parameter in determining the optimal operating conditions and guiding the redesign process. Likewise, the investigation of deviations from optimal settings emphasizes potential applications of this burner design in industrial processes.