SUSTAINABLE BUS 2-2023

OUTLOOKS
HYDROGEN: FROM SOURCES TO USES
Figure 1. Schematic representation of sector coupling and H2
infrastructure. Source: EMCEL
BEHIND THE HYDROGEN DISPENSER…
Handling hydrogen in
enclosed spaces involves
three basic rules. The
first is that good ventilation
must be provided
in the rooms. Secondly,
in general, sources of
ignition should be avoided
in rooms. Grounding
of vehicles is a general
requirement for refueling.
Third and last, for indoor
hydrogen applications,
H2 sensors should be
used. These measure
the percentage hydrogen
concentration in the air
and warn when critical
values are exceeded. At
the same time, this activates
safety measures.
Figure 3. Process diagram of a hydrogen filling station. Source: EMCEL
the H2 supply, the compressor unit, the
storage tank and the dispenser.
The dispenser represents the interface
between the filling station and the vehicle
to be refueled. A technically tight connection
between the vehicle (fuelling nipple)
and the dispenser (fuelling nozzle)
ensures a safe refueling process without
operationally induced gas releases in the
vehicle area. This means that hydrogen
dispensers - just like natural gas dispensers
- can also be installed indoors (e.g.
just before car washes or in the workshop
lanes of bus companies).
In order to achieve higher refueling
speeds and at the same time ensure a safe
refueling process, a cooling unit is usually
provided. This intervenes after the last
compression stage immediately before
the dispenser. Depending on the refueling
protocol and ambient conditions, the
hydrogen to be refueled is cooled down to
a temperature of -40°C.
Making refueling safe
Safe operation of the hydrogen refueling
station is ensured by compliance with regulations,
codes and standards. Not only
the handling of the hydrogen itself, but also
electrical, mechanical and weather-related
aspects have to be considered.
Common safety features for hydrogen re-
fueling stations are:
- ATEX protection (explosion protection)
- lightning protection
- fire protection
- technical tightness of H2 components
- collision protection.
In certain plant areas, the release of hydrogen
cannot be ruled out, but is even permissible
or provided for in terms of safety (e.g.,
for overpressure relief). With regard to explosion
protection, an explosion protection
concept must be drawn up. The areas in
which potentially explosive gas mixtures
can occur must be designed safely or clearly
marked. Attention must be paid to the
special personnel protection equipment required
when working in ATEX zones and to
the use of ATEX equipment (non-sparking).
With regard to protection against fires, fire
barriers can be erected around the trailer
parking areas and other hazardous areas.
In the event of a fire, they are intended to
protect the surrounding plant areas from fire
and heat radiation.
H2 AND NATURAL GAS, SIMILARITIES AND DIFFERENCES
Hydrogen H2 Methane CH4
Lower and upper concentration limits for ignition 4 %...74 % 4,1 %…16,5 %
Ignition temperature 560°C 575…640°C
Minimum ignition energy 0,02 mJ 0,28 mJ
Figure 2. Substance data of hydrogen in comparison with natural gas. Source: EMCEL
With regard to the design and installation
of the H2 components, it is important that
pipelines, containers, valves and fittings
are technically tight or permanently technically
tight (The definition used in this
article refers to the German TRGS 722 -
Technical Rules for Hazardous Substances).
In the case of permanently technically
tight components, no gas releases are
to be expected. In the case of components
that are technically tight, gas releases can
also (infrequently) occur. Here, redundant
safety measures are applied if necessary
(e.g.: regular inspection by leakage test
procedures).
Safe handling of hydrogen
Handling hydrogen in enclosed spaces
involves three basic rules. The first is
that good ventilation must be provided in
the rooms. Otherwise, hydrogen leakage
could result in elevated concentrations in
the enclosed spaces. Ventilation systems
provide increased air exchange, which
minimizes or eliminates the risk of flammable
concentrations forming. Secondly,
In general, sources of ignition should be
avoided in rooms. This applies in particular
to gas workplaces and ATEX zones.
Here, for example, grounding of vehicles
is a general requirement for refueling.
This can take place either by means of
a grounding clamp or through the fuel
nozzle and the tank hose itself, if certain
In order to achieve higher
refueling speeds and
ensure a safe refueling
process, a cooling unit is
usually provided. This intervenes
after the last compression
stage immediately
before the dispenser. The
hydrogen to be refueled is
usually cooled down to a
temperature of -40°C.
limits for insulation resistance are taken
into account. Alternatively, a conductive
ground can ensure that equipotential
bonding is established. Another example
of avoiding ignition sources is the use of
ATEX equipment, for example for emergency
lighting. Third and last, for indoor
hydrogen applications, H2 sensors should
be used. These measure the percentage
hydrogen concentration in the air and
warn when critical values are exceeded.
At the same time, this activates safety measures.
Hydrogen, safety is possible
Safe operation with hydrogen is already
possible today in exactly the same way
as for other fuels. The similarity to natural
gas makes it easier to switch to this
technology, as approaches and safety concepts
can be easily transferred. H2 refueling
stations can also be operated safely
and reliably indoors, provided appropriate
safety measures are applied. For the
construction of a hydrogen filling station,
it is advisable to draw up a safety concept
tailored to the specific application. In this
way, cost-effective implementations can
be achieved in a targeted manner!
Nicolò Queirazza, Lennart Heine
(EMCEL GmbH)
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