Design and Optimization of an Emergency Auto-thermal Burner for Liquid Hydrogen

The adoption of hydrogen has been largely indicated as a feasible solution to support society in achieving its ambitious targets for a low-carbon future. The increased knowledge in liquefaction techniques has encouraged the study of technological solutions based on liquid hydrogen (LH2). Moreover, handling and distribution under cryogenic conditions represent attractive options due to the elevated energy density of LH2. Despite these advantages, the bottleneck for its widespread adoption is represented by safety aspects. Considering that an LH2 tank truck has a probability of suffering a car accident like all other road vehicles, an emergency auto-thermal burner has been designed in this work. This safety system has the purpose to dispose of the content of a tank truck to avoid the loss of containment. The disposal process includes the vaporization and pre-heating of the LH2, the mixing with ambient air, and its combustion. This device is completely self-supporting since the heat required to vaporize the LH2 is entirely provided by the combustion of the fuel itself. Firstly, the equation of energy balance around the burner was numerically solved to estimate the temperature of flue gases. Then, inner and outer heat transfer coefficients were determined for each section of the coiled-tube heat exchanger. Finally, the heat transfer surface was calculated. The spontaneous conversion between two spin isomers of hydrogen was considered. From the perspective of the heating process, the enthalpy of conversion represents an additional energy request. If the decrease of para-hydrogen fraction was neglected, the length of the heat exchanger would be significantly underestimated. Based on the obtained results, it is possible to conclude that the designed device can be transported on-site and started up easily, making it suitable for emergency response.