H2Tech - Q1 2021 - 36

SAFETY AND SUSTAINABILITY
shown in FIG. 4, and photographs from
their test are provided in FIG. 5.
Golub et al.12 performed similar experiments accompanied by numerical
simulations. Some of their results are
summarized in FIG. 6. The X-axis " L " value
in FIG. 6 is the length of the low-pressure
chamber in their apparatus. The primary
conclusions from their work were that:
* The possible reason for self-ignition
is heating by the primary shock wave
* Self-ignition occurs if the source H2
pressure is on the order of 150 bar-
400 bar, the temperature of the H2
and the air is 300K or more and the
hole diameter is greater than 3 mm.
Ongoing experimental efforts. Baker

Engineering and Risk Consultants Inc.
(BakerRisk) is actively addressing the
unique safety challenges of H2 and the
rapid growth of H2 infrastructure. As part
of that support, BakerRisk is performing a series of internal testing programs
focused on H2 dispersion and ignition

Why does it matter to hydrogen infrastructure? Significant debate has

emerged over the past several years about

the potential magnitude of H2 release
events with regard to VCEs. Testing and
numerical simulations performed by
BakerRisk and others have demonstrated
that VCEs due to H2 releases can be more
severe than with most other flammable
materials (e.g., methane, propane, etc.8).
Specifically, H2 is a high-reactivity fuel that
is more likely to undergo a deflagration-todetonation transition (DDT). Testing by
BakerRisk in both unconfined and confined test rigs has shown that DDTs can
occur with lean (i.e., non-optimal) H2-air
mixtures.13,14 Numerical evaluations have
been performed to examine the potential
for DDTs in ambient vaporizers.15 The potential for explosions due to H2 jet releases
has also been considered.16,17
BakerRisk has also undertaken separate investigations of H2 applications as a
fuel source and of H2 ignition probabilities.18,19 These studies indicate that the
hazards/risks of H2 usage may have been
misunderstood until recent years, but that
our understanding is rapidly developing.
Takeaway. Investigations over the past
several years have begun to provide clarity
on previous misconceptions about H2 igni-

4-mm nozzle

PO, bar

250
225
200
175
150
125
100
75
50
25
0

probability. The primary goal of these
tests, which are being conducted at one
of BakerRisk's test facilities, is to study the
ignition probability of H2 under a range of
typical operational conditions and release
sizes. A secondary goal is to compare test
cases of gaseous H2 releases to dispersion
models to validate or improve those models, as necessary.
This series of H2 dispersion and ignition tests will be run using the BakerRisk
cylinder skid dispersion rig (FIG. 7), which
allows the team to disperse a variety of gases without significant modifications to existing and validated rigs. The cylinder skid
dispersion rig was built with 316 stainless
steel to allow for compatibility with a diverse range of materials and can withstand
supply pressures up to 3,000 psig. Testing
is being performed under a variety of release conditions, pressures and flowrates.

100

60
80
Length of extension pipe, mm

100

120

140

FIG. 4. Critical conditions for spontaneous ignitions inside the extension tube downstream
of the rupture disc.

P, bar

Ignition, jet fire
No ignition

40
20

Self-ignition did not occur
Self-ignition occurred

120
L, mm

160

200

FIG. 6. Experimental results showing
dependence of minimal reservoir pressure
on the external tube length when
self-ignition occurs.

FIG. 5. Development of the H2 jet on the nozzle exit (4-mm nozzle, 200-bar initial pressure)
in experiments with (right) and without (left) rupture disc in the flow path from the leak valve
to the nozzle exit.

36 Q1 2021 | H2-Tech.com

FIG. 7. The cylinder skid dispersion rig at the
test facility, prior to commissioning.

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H2Tech - Q1 2021

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