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Hydrogen can be produced either by water electrolysis using electricity or by steam
reforming of natural gas. After purification and compression, hydrogen is then delivered by pipe
or in transportable containers or trailers if not directly produced on site.
Electrolysers are systems producing hydrogen from water and electricity.
The hydrogen gas produced using electrolysis technology can then be utilized immediately
or stored for later use. As of today, electrolysers are most often used in industrial
applications; most of them have small to medium capacities (production of hydrogen smaller
than 500 Nm3/h), but also very large installations exist, producing more than 20.000 m3/h.
Electrolysers can be easily regulated and do not emit anything else than O2 and H2.
They can produce very pure hydrogen at elevated pressures.
Reformers are systems producing hydrogen from natural gas, from steam and heat.
They are most often used in industrial applications; their capacity ranges from a few hundred
to more than 100 000 Nm3/h. Reformers are operated 24/7 at constant load and do emit CO2.
The produced hydrogen is not very clean and at atmospheric pressure.
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In an electrolyser cell, electricity causes dissociation of water into hydrogen and oxygen
molecules. An electric current is passed between two electrodes separated by a conductive
electrolyte or “ion transport medium”, producing hydrogen at the negative electrode (cathode)
and oxygen at the positive electrode (anode).
Two main technologies of electrolysers exist: electrolysers based on the
- Alkaline electrolysis process and electrolysers based on the
- PEM (Proton Exchange Membrane) electrolysis process.
Their technical maturities, their operating temperatures and their electrolytes are different.
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Alkaline electrolysis: it is the technology which is most often used in industrial applications.
The electrolyte is a potassium hydroxide solution. The operating temperature ranges
from 60 to 100°C and the operating pressure ranges from 1 to 30 bar. As their operating
pressure is low, alkaline electrolysers take a lot of space.
Their efficiency is around 65%.
Figure 128: Electrolyser developed by Norsk Hydro
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The key component of the electrolysers is its membrane – electrode system.
The membrane is made of polymer, and the electrodes use catalysts
madeof porous precious metals. At the anode, the water feed is broken down in oxygen,
electrons and protons. Protons migrate through the membrane to the cathode, where
they are reduced in hydrogen molecules, while electrons migrate via the external circuit
to the cathode where they combine with protons. Membranes show good chemical stability,
mechanical resistance, protons conductivity, and gas separation. The main advantage of PEM
electrolysers is that they can operate under load changes conditions and under high resistance).
On the other hand, the costs of the electrolyte and of the electro catalysts are high.
Figure 129: PEM electrolyser
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Hazardous situations
Prevention or mitigation
measures
Loss of segregation within system of H2 and O2 produced –
process pressure is an aggravating factor as this increases
amount of reactants in the system and burst pressure of
equipment
Process reliability and detection
of O2 in H2
Formation of flammable mixture in container due to a H2 leak
Permanent ventilation and H2
detection
Electrical safety, fire detection
Fire due to failure/overheating of high current electrical
components
In case of liquid electrolyte: short circuit from electrolyte leaks
Quality of assembly, periodic
inspection
In case of liquid electrolyte: corrosive electrolyte leaks
Quality of assembly, periodic
inspection
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ISO 22734-1:2008 Hydrogen generators using water electrolysis process
Part 1: Industrial and commercial applications, Edition 1
ISO 22734-2 Hydrogen generators using water electrolysis process
Part 2: Residential applications, Edition 1
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In a first step, about 2% of hydrogen is added in the natural gas. This process gas is then
pre-heated to 350°C. As the natural gas contains sulphurated impurities, a desulphurization step is
required. The desulphurated process gas is then mixed with steam and pre-heated to about
500°C.
The reformer is a cylindrical vertical oven. The process gas flows down the oven through the
reforming tubes filled with catalyst. Catalytic reactions produce syngas (mix of hydrogen,
carbon monoxide, carbon dioxide; some water and methane from the process gas remain in the
syngas). The reactions producing hydrogen are:
CH4 + H2O → CO + 3H2
CO + H2O → CO2 + H2
Steam methane reforming reaction is very endothermic. The syngas flowing out the reforming tubes
at the bottom of the oven has a temperature of about 850°C. It is then cooled down to about 350°C,
and flows through a carbon monoxide converter where a catalytic reaction produces hydrogen
and carbon dioxide from water and carbon monoxide. The gas is cooled down to 35°C;
remaining steam is condensed. The gas leaving the cooling device contains mostly hydrogen (more
than 70%), and some impurities (mostly carbon dioxide) which are removed in a purification unit.
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9
4
3
8
5
7
6
2
1
Figure 131: Steam methane reforming
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The main elements which should be considered when assessing the safety of reformer
units are the burner, its flame and the combustion quality, the reforming tubes and the
steam production unit.
The main hazards for the burner, its flame and the combustion quality are:
An explosive atmosphere might be ignited by the burner
An increase of the flame temperature and thus an increase of the temperature of the gases
would damage the materials of the oven and of the reforming tubes.
An incomplete combustion of gases in the combustion chamber would lead to the formation of
deposits in the exchangers, and the composition of the flue gases would not be in
compliance with the composition specified in the standards.
The main hazard for the reforming tubes is the formation of a leak on these tubes because
of an early ageing of the reforming tubes. This could be caused by an inhomogeneous
distribution of the process gas and of the heat between the reforming tubes, which would lead to
an inhomogeneous distribution of the temperatures on these tubes and thus to their early ageing.
The main hazard for the steam production unit is an abnormal pressure increase.
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ISO 16110-1:2007 Hydrogen generators using fuel processing technologies
Part 1: Safety, Edition 1
Scope: packaged, self-contained or factory matched hydrogen generation systems with a capacity
of less than 400 m3/h at 0 °C and 101,325 kPa
This part of ISO 16110 is applicable to stationary hydrogen generators intended for indoor
and outdoor commercial, industrial, light industrial and residential use.
It aims to cover all significant hazards, hazardous situations and events relevant to
hydrogen generators, with the exception of those associated with environmental compatibility
(installation conditions), when they are used as intended and under the conditions foreseen
by the manufacturer.
NOTE A list of significant hazards and hazardous situations dealt with in this part of ISO 16110
is found in Annex A.
This part of ISO 16110 is a product safety standard suitable for conformity assessment as
stated in IEC Guide 104, ISO/IEC Guide 51 and ISO/IEC Guide 7.
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Hydrogen tranport by pipelines has been used for many years for supply
to very large consumers, such as refineries. Compressed hydrogen is fed in metallic pipelines,
which are either above-ground piping systems or underground piping systems.
In the case of underground piping systems, hydrogen pipe is run in an open trench
covered by a grating.
Most of the pipes used in hydrogen installations are made of stainless steel. Pipes are not
made of plastic, or of any metallic material which is not resistant to high temperatures.
Rotterdam
Hydrogen Pipelines
Germany
Dordrecht
Netherlands
Zeebrugge
Duisburg
Antwerp
Brussels
Lille
Mons
Belgium
Charleroi
Liège
France
Maubeuge
Herne
Düsseldorf
Genk
Ghent
Marl
Dortmund
Krefeld
Dunkerque
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Rheinberg
Geelen
Leverkussen
12 networks worldwide
F/Be/NL: 810 km (100 bar)
Germany : 240 km (200 bar)
Figure 132: Hydrogen
pipeline network of
Air Liquide
in Northern Europe
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Hazard
Safety measures
Rupture of pipes and fittings because Hydrogen compatible materials should be chosen.
of hydrogen embrittlement
Piping must be externally coated to an approved specification, to protect against
soil corrosion.
Rupture of the pipe material due to
lightning strikes or ground fault
conditions
Electrical continuity between underground hydrogen piping and above ground
piping, or other metal structures, should be avoided.
All above-ground pipelines shall have electrical continuity across all connections,
except insulating flanges, and shall be earthed at suitable intervals to protect
against the effects of lightning and static electricity
Rupture due to external forces
Piping should not be exposed to external forces which can cause a failure or
dangerous situation. The main cause of pipe rupture is attack by external
operation (e.g. when a mechanical digger knocks on a pipe).
Hazards specific to underground
piping
It is preferable to have no flanged or other mechanical joints underground.
Only gaseous hydrogen pipes with welded joints may be buried.
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Corrosion for underground piping
Table 41: Safety measures for pipes
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For consumptions of up to a 200 Nm3/h, hydrogen is transported in pressurized or liquid form
in transportable containers or trailers. For larger consumptions, hydrogen is produced at the
site of use (by electrolysis or steam reforming). Compressed gaseous hydrogen is transported
by tube trailers which consist of steel tubes or cylinders at 200 to 250 bar. A typical tube trailer
has a capacity of 400 kg. This capacity can be largely increased by use of composite materials.
Figure 133: Examples of compressed hydrogen tube trailers
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In order to increase its density, hydrogen may be liquefied and transported by
liquid hydrogen tankers. However, storing liquid hydrogen over a long period
of timeis challenging because of its rapid evaporation in case of parasitic heat input.
Tankersare insulated, and they may have large capacities exceeding 60 000L.
Figure 134: Liquid hydrogen tanker
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The following safety devices are used in trailers or tankers:
Safety relief valves and rupture bursting discs protect the vessels and pipes from an excessive
pressure which might cause their rupture.

Safety relief valves start to open at their set pressure.
They re-set when the pressure is at 90% of the set pressure.

Rupture bursting discs are metal foil discs which are designed to rupture at a set
pressure. They do not re-set once they have burst.
Emergency valves prevent any loss of hydrogen in case of pipes failures, or in case of an accident
during the trailer / tanker filling or discharge.
Vacuum safety devices protect the outer jacket from bursting and / or the inner vessel from
collapsing in the case of a product leak into the vaccum interspace (between the inner vessel and the
outer jacket).
Anti tow-away devices can be used to prevent the vehicle from moving when the road transport
equipment control cabinet doors are open OR when a product transfer and / or vent hose is
connected to the road transport equipment pipework coupling.
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Road Vehicle Emergency and Recovery, IGC Doc 81/06/E, Revision of Doc 81/01,
European Industrial Gases Association AISBL
ISO 10961 This International Standard specifies the requirements for the design, construction,
testing and initial inspection of a transportable cylinder bundle. It is applicable to cylinder
bundles containing compressed gas, liquefied gas and mixtures thereof. It is also applicable to
cylinder bundles for acetylene
Trailers EN 13807
This European Standard specifies the requirements for the design, manufacture, identification
and testing of a battery vehicle. It is applicable to battery vehicles containing compressed gas,
liquefied gas and mixtures thereof. It is also applicable to battery vehicles for dissolved
acetylene. This European Standard does not apply to the vehicle chassis or motive unit or to
multi-element gas containers (MEGC's), pressure drums and tanks. This standard is primarily
for industrial gases other than Liquefied Petroleum Gases (LPG) but may also be used for LPG.
However for dedicated LPG cylinders, see standards prepared by CEN/TC 286 Liquefied
petroleum gas equipment and accessories.
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Hydrogen installations are usually designed to perform two functions:
(i)storage of hydrogen delivered by road and
(ii)(ii) distribution of hydrogen to point of use in the required condition of pressure and
temperature.
The storage function is typically performed in one of the following two ways:
1.Even exchange of containers:
delivery and storage performed by means of transportable hydrogen containers: these
are either bundles of cylinders unloaded for small hydrogen consumptions, or trailers for large
hydrogen consumptions. In order to ensure continuity of supply, two hydrogen containers are
connected at all times to the distribution system. The latter includes a device which switches
automatically supply to the second container when the first one is depleted
(i.e. when source pressure falls below a specified threshold). The supplier is informed of this switchover and delivers a full container well before depletion of the container in use. When this occurs, the
installation switches automatically to the newly delivered container and a new delivery takes place
to replace the newly depleted container, and so on.
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Figure 135: Block diagram for hydrogen supply from two hydrogen trailers
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2.
Product transfer:
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Hydrogen is transferred by
pressure difference from the
delivery trailer to a stationary
hydrogen storage tank. With
this mode of supply, the on-site
storage pressure needs to be
significantly lower than the
pressure in the delivery trailer
(e.g. 50 bar vs 200 bar), in
order to be able to take
sufficient advantage of the
trailer capacity. See below for
an example of flow diagram of
gas transfer.
Figure 136: Flow diagram for gas transfer
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The main risk associated with hydrogen supply is that of tearing the high pressure
flexible hoses as a consequence of moving a container that is still connected to the
fixed installation. Also the flexible hose is a limited lifetime component hence requiring
preventive replacement at fixed time intervals.
The following safety measures are implemented:
Prevention of movement of trailers that are connected to the installation,
e.g. by locking the trailer’s brakes when the high pressure hose is connected to the trailer.
Isolation valve on the trailer located on the forward side. In case of high pressure hose
rupture, the trailer can be safely isolated in order to prevent it from being emptied
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H2 supply system Installation:
ISO/DIS 20100 clause 5.2 Gaseous hydrogen supply by
tube trailers and Multi Cylinder Packs (MCPs) and 14 Separation distances
List of all the standards of TC 58 and TC 197 relative to vessels/tanks
ISO 15399: Gaseous hydrogen. Cylinders and tubes for stationary storage
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