Ultrasonic Time-of-flight Measurement of Hydrogen Blending Ratios for Industrial Combustion Applications

Hydrogen blending offers significant potential for decarbonizing natural gas-based thermal processes, particularly in the steel and cement sectors. Due to its distinct combustion properties compared to natural gas – such as lower minimum air requirements and altered flame speeds – the hydrogen fraction of the fuel must be monitored for combustion control. In this study, we present an ultrasonic time-of-flight measurement system for hydrogen concentrations of 0–40% in natural gas. The system is verified with test gas mixtures at laboratory scale and validated in a technical-scale setup using a real blower burner (< 60 kW). We evaluate uncertainty of the hydrogen fraction measurement and analyze the influence of varying natural gas compositions. We show that standard uncertainties below 4% can be achieved without knowledge of the specific natural gas composition. Our results provide insights for measurement system design and support the safe application of hydrogen in thermal systems for industrial processes.