Simulation of Detonation after an Accidental Hydrogen Release in Enclosed Environments

An accidental hydrogen release in equipment enclosures may result in the presence of a detonable mixture in a confined environment. Numerical simulation is potentially a useful tool for damage assessment in these situations. To assess the value of CFD techniques, numerical simulation of detonation was performed for two realistic scenarios. The first scenario starts with a pipe failure in an electrolyzer, resulting in a leak of 42 g of hydrogen. The second scenario deals with a failure in a reformer where 84 g of hydrogen is released. In both cases, dispersion patterns were first obtained from separate numerical simulation and were then used as initial condition in a detonation simulation, based upon the reactive Euler's equations. Energy was artificially added in a narrow region to simulate detonative ignition. In the electrolyzer, ignition was assumed to occur 500 ms after beginning of the release. Results show a detonation failing on the top and bottom side but propagating left and right, before eventually failing also. Average impulse was 500 Ns/m². For the reformer, three cases were simulated, with ignition 1.0, 1.4 and 2.0 seconds after the beginning of the release. In two cases, the detonation wave failed everywhere except in the direction of the release, in which it continued propagating until reaching the side wall. In the third, the detonation failed everywhere at first but later, a deflagration to detonation transition occurred, resulting in a strong wave that propagated rapidly toward the side wall. In all three cases, the consequences are more serious than in the electrolyzer.