Test stand at the BAM TTS, size of test rig 18 m x 5 m x 4 m (Length x Width x Height)
Source: BAM
For industrial applications dealing with hydrogen, the definition of safety distances and the assessment of possible hazards emanating from releases is mandatory. Since hydrogen is usually stored and transported under pressure, one scenario to be considered is the momentum driven release of hydrogen from a leakage or safety valve/blow off pipe with subsequent ignition. In this scenario, the emitted heat radiation from the resulting jet flame to the surroundings has to be determined to define adequate safety distances. For hydrocarbon flames, different jet flame models are available to assess the hazards resulting from an ignited jet release. Since hydrogen flames differ from hydrocarbon flames in their combustion behavior, it has to be checked if these models are also applicable for hydrogen. To evaluate the accuracy of these models for hydrogen jet flames, tests at large-scale are carried out at the BAM Test Site for Technical Safety (BAM-TTS). Herein, the flame geometry and the heat radiation at defined locations in the surroundings are recorded for varying release parameters such as release pressure (up to max. 250 bar) and mass flow (up to max. 0,175 kg/s) at an outlet diameter of 30 mm. The challenge here is the characterization of the flame geometry in an open environment and its impact on the thermal radiation. Existing heat radiation data from the literature are mostly based on unsteady outflow conditions. For a better comparability with the steady state jet flame models, the experiments presented here are focused on ensuring a constant mass flow over the release duration (currently 120 s) to obtain a stationary jet flame. In addition, stationary outflow tests with hydrocarbons (methane) were also carried out, which are intended to serve as reference tests for checking flame models based on hydrocarbon data. The comparison of the flame geometry shows that hydrogen jet flames with the same outlet mass flow have a greater flame length (average deviation of 15%) but a smaller flame diameter than methane jet flames (average deviation of 17%). Conclusions regarding thermal radiation show that the proportion total combustion energy emitted as thermal radiation (radiant heat fraction) is lower for hydrogen (0,04-0,09) than for methane (0,06-0,1). A comparison of the surface emissive power (SEP), which describes the released energy over the jet flame surface, shows a SEP range of 7 kW/m²-15 kW/m² for hydrogen and 3 kW/m²-9,5 kW/m² for methane.
Large-scale investigations of the thermal radiation of hydrogen jet flames
Christopher Bernardy, Abdel Karim Habib, Martin Kluge, Bernd Schalau, Hanjo Kant, Marcel Schulze, Alessandro Orchini
Journal of Loss Prevention in the Process Industries, Volume 94, April 2025