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hydrogen: all at sea

both downwards and horizontally as well departure from the downwind
as into a confined space representing a direction of about 90o
tank connection chamber. Peak gas concentration versus the peak
All experiments were conducted within dip in temperature, giving a nominally
a 250m exclusion zone and controlled linear relationship, worsening as the
remotely. This followed the method for concentration gets higher
purging and cooling the pipe that went Higher concentrations at higher
from gaseous nitrogen (N₂) to liquid positions above ground level
nitrogen (LN₂) to gaseous helium (He₂) to LFL was not exceeded in downward
cold gaseous hydrogen (H₂) to LH₂. releases beyond 30m from the
Measurements focused on the release point and 50m in the
temperature of the surface and horizontal releases.
subsurface of the concrete close to the
release while dispersion measurements The relationship between the
using oxygen sensors were taken further peak concentration and the peak
afield. The oxygen sensors measured temperature drop across several
the hydrogen gas concentration by experiments was further compared to
examining the depletion of oxygen in the predictions from GasVLE, a fluid
the atmosphere. Two of the experiments properties calculation tool from DNV,
were ignited after a delay to gather the predictions are slightly below that
information on thermal radiation and of the actual observations. This may
overpressure. be because the GasVLE model does not
include heat transfer from the ground,
RESULTS possibly evident in the measurements.
Using the legacy British Gas model At the point of ignition there is an
FROST and the DNV PHAST models, explosion effect creating an initial
prediction of the vapour quality by expanding fireball which can give
mass and outflow were considered, rise to local dynamic overpressures
with knowledge of the geometry of the with the potential to cause harm.
release point orifice and the saturations At all measurement locations, in all
conditions near to it. unconfined ignited experiments, the
The liquid/vapour fractions along the peak pressure did not exceed 30mbar
pipe during releases were calculated in the horizontal jet and around about
based on the pressure decay and 15mbar in the downwards jet. Within
assuming isenthalpic expansion. the confined space when releases
Releases in all experiments produced were ignited, significantly higher
high liquid mass fractions (i.e., the overpressure events were observed –
proportion of the mass flowing in as would be expected.
the pipe being in the liquid phase) The releases conducted as part of
with experiments being driven above the programme provide a valuable,
saturation pressure in the tanker extensive and unique dataset in relation
producing higher liquid mass fractions to the phenomena contributing to
(i.e., little or no flashing in the pipe). the severity of events following a loss
One of the key considerations when of containment of liquid hydrogen. AFTER A LARGE VOLUME RELEASE OF LH2 WAS CONDUCTED, THE
assessing the risk of releases is how The outdoor release data has been ATMOSPHERE IN THE CHAMBER WAS ALLOWED TO NATURALLY
much of the two-phase flow ends up compared to predictions from existing DECAY INTO A REACTIVE MIXTURE BEFORE BEING IGNITED WITHIN
THE CHAMBER. SOME POLYSTYRENE BOARDS USED FOR INSULATING
on the floor, forming a pool, perhaps, software models and found to be of a THE EXPLOSION VENT CAN BE SEEN BEING EJECTED FROM THE
or raining out from the jet. Taking high quality and suitable for further CHAMBER. SIGNIFICANT DAMAGE TO THE FLOOR OF THE CHAMBER AND
THE LIGHTWEIGHT VENTILATION MAST CAN BE SEEN
the measurements of the surface and model development/validation.
subsurface temperature of the concrete Despite being a clean fuel, concern e-fuels such as ammonia and synthetic
and in the experiments allowed DNV to surrounds its chemical and physical jet fuel must be considered.
conclude there was no evidence for any properties and the gaps in engineering Government incentives, similar
LH₂ beyond 0.5m from the releases in techniques, tools and implementation to those given to renewables, are
the downward releases conducted onto experience and the potential impact on needed to eliminate risk through
concrete in the programme and there safety. Further investigation and model comprehensive R&D, stimulate
was zero evidence of any rainout in the analysis is recommended. technology development, and accelerate
horizontal releases. uptake of hydrogen and e-fuels.
Having set or determined the source HIGH HOPES FOR HYDROGEN Maritime, aviation, and heavy
conditions by looking at the outflow, Hydrogen is one of the most suitable industry thus retain high unabated fossil
the dispersion and ultimately, the lower solutions to contribute to the fuel shares towards 2050, slowing the
flammable limits (LFL) of the dispersing replacement hydrocarbons in the transition and significantly impeding the
cloud was analysed. The trends in future and its consumption is expected achievement of the Paris Agreement.
the experimental results were also to grow significantly over the next
represented in the model results: three decades. As direct hydrogen Download DNV’s latest Energy
Reducing concentration with distance use is often not suitable for ships and Transition Outlook by visiting
Reducing concentration with radial aircraft, hydrogen derivatives and www.eto.dnv.com/2021

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