Electrostatic Ignition (Summary of experiment series E4.3 results)

Work package four of the PRESLHY project focuses on ignition phenomena. This report summarises the experimental series E4.3, which focuses on the propensity for an electrostatic charge capable of igniting a hydrogen cloud to be generated during a release, or accidental spill scenario. Seven experiments measuring the electric field of a multiphase hydrogen jet were conducted at the HSE Science and Research Centre. Current measurements on an electrically isolated section of steel pipework were also taken during a total of 30 large scale releases. The results from the plume measurements indicate that the multiphase hydrogen jet itself does not create a significant charge, but certain interactions with the air can cause intermittent spikes in field strength. In particular, air in the pipework being ejected and solidified air forming around the release point, breaking off and flowing downstream appear to be the cause of the electrical fields measured in these experiments. This effect could be larger with different initial conditions either at the nozzle or in the tanker. The wall current measurements were more consistent, as the ability for LH 2 to induce a current on a section of electrically insulated pipework was clearly demonstrated. This charge is a complicated function of the phase of LH 2 in the pipework, the turbulence of the flow, and the resistance to ground of the section of the pipework. Frost formation on the outside of the pipework dynamically changed the resistance to ground throughout each trial, making interrogation of the results difficult. The experiments show that electrostatic charges do pose a credible hazard when considering LH 2 facilities. The charging, however, does not form inside the hydrogen, but on the substances or objects that the hydrogen interacts with. For a fixed facility, maintaining continuity to earth, paying attention to objects in the potential path of a release, would limit the likelihood of electrostatic charging and therefore limit the hazard.PRESLHY项目第四工作包聚焦点火现象。本报告总结了实验系列E4.3，该系列聚焦于氢气释放或意外泄漏场景中，生成足以引燃氢云的静电荷的可能性。研究团队在健康与安全执行局（Health and Safety Executive，HSE）科学研究中心开展了7项针对多相氢射流电场的实验。此外，在总计30次大规模释放实验中，还对一段电气隔离的钢制管道的电流进行了测量。 羽流测量结果表明，多相氢射流本身不会产生显著电荷，但与空气的特定相互作用会导致电场强度出现间歇性尖峰。具体而言，管道内空气被喷出、释放点周围形成的固态空气脱落并随下游气流运动，似乎是本次实验中测得电场的成因。若喷嘴或储罐内的初始条件发生变化，该效应可能会更为显著。 管壁电流的测量结果更为一致，因为实验清晰证明了液氢（Liquid Hydrogen，LH2）可在一段绝缘管道上感应出电流。该电荷是管道内液氢相态、流场湍流程度以及该段管道接地电阻的复杂函数。每次实验过程中，管道外壁结霜都会动态改变接地电阻，这给实验结果的解析带来了困难。 实验结果表明，在涉及液氢（LH2）设施的场景中，静电荷确实构成了切实的安全隐患。不过，静电荷并非在氢气内部产生，而是在氢气与之发生相互作用的物质或物体表面形成。对于固定式设施而言，保持系统接地连续性，并关注释放路径潜在涉及的物体，可降低静电荷产生的可能性，从而减轻相关危害。