Hydrogen can be produced either by water electrolysis process or by steam reforming of natural gas . Hydrogen is then delivered by pipe or in transportable containers or trailers . Below are described the systems involved in hydrogen production and distribution; the safety measures for these systems are reviewed.
1.1.1.1
Description
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 Nm 3 /h).
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.


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 70 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%
(efficiency related to the LHV).
Figure 1: Electrolyser developed by Norsk Hydro
(Source : Alphea Hydrogen, 2005, “Electrolyseurs de grande capacité”)
Note: operating pressure ranging from 1 to 12 bar; capacities ranging from 10 to 377 Nm 3 /h of hydrogen.


PEM electrolysis : the key component of the electrolysers is its membrane – electrode system. The membrane is made of polymer, and the electrodes use catalysts made of 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.
Figure 2: PEM electrolyser
(Source: Alphea Hydrogen, 2005, “Electrolyseurs de grande capacité” from Meng N., Leun M., Sumathy K. Leun D.Y.C., 2004, “Water electrolysis – a bridge between Renewable Resources and Hydrogen”, Hyforum proceedings, p 475-480)
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 pressures (because of the membrane resistance). On the other hand, the costs of the electrolyte and of the electrocatalysts are high .

Figure 3: Alkaline electrolyzer vs PEM electrolyzer
(Source: Siemens)
The electrolysis cell(s), and electrical, gas processing, ventilation, cooling and monitoring equipment and controls are contained within the hydrogen generator enclosure. Gas compression and feed water conditioning and auxiliary equipment may also be included.

1.1.1.2
Safety measures and coverage by standards and certification
Main hazards
Main potentially hazardous situations that need to be prevented or mitigated by design and operating requirements”:
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
Fire due to failure/overheating of high current electrical components
Electrical safety, fire detection
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
Coverage by standards
The hazards previously listed should be taken into account in the design of the electrolysers, so that electrolysers are safe by design. The design of electrolyser is well covered by international standards: the construction, safety and performance requirements of packaged hydrogen generators using the electrolysis process to produce hydrogen are described in the standard ISO 22734 . This standard specifies also the tests methods which shall be used to carry out qualification tests or routine tests. ISO 22734 consists of two parts: industrial & commercial applications and residential applications (ISO 22734-1 - Industrial). There are additional safety measures for residential applications (ISO 22734-2 - Residential).

1.1.2.1
Description
Reformers are systems producing hydrogen from natural gas, from steam and heat.
Reformers are most often used in industrial applications; their capacity ranges from a few hundred to more than 100 000 Nm 3 /h .
In a first step, about 2% of hydrogen is added in the natural gas which will feed the
steam reforming unit (step 1 in Figure 4 ). This process gas is then
pre-heated to
350°C
(step 2 in Figure 4 ). As the natural gas contains sulphurated impurities which
would poison the catalyst in the reforming unit, a desulphurization step is required
(step 3 in Figure 4 ).
The desulphurated process gas is then mixed with steam and preheated to about 500°C
(step 4 in Figure 4 ), before
feeding the reformer . The reformer is a cylindrical vertical oven. Reforming tubes under pressure are heated by a burner which is at the top of the oven. The process gas flows down the oven through the reforming tubes filled with catalyst
(step 5 in Figure 4 ).
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:
CH
4
+ H
2
O → CO + 3H
2
CO + H
2
O → CO
2
+ H
2
Steam methane reforming reaction is very endothermic: the process gas is heated as it flows down the oven. 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
(step 6 in Figure 4 ), and
flows through a carbon monoxide converter where a catalytic reaction produces hydrogen and carbon dioxide from water and carbon monoxide
(step 7 in Figure 4 ). The gas is then
cooled down to 35°C ; remaining
steam is condensed (step 8 in Figure 4 ). 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
(step 9 in Figure 4 ).

9
3
4
5 7
8
6
2
1
Figure 4: Steam methane reforming
(Reference: Ray Elshout, Energy Systems Engineering, “Hydrogen Production by
Steam Reforming”, edited on the website of Chemical Engineering Processing, by
Scott Jenkins)

1.1.2.2
Safety measures and coverage by standards and certification
Main hazards
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 in the steam production unit.

Safety measures
The following safety measures can be implemented to reduce the risks:
Table 1: Safety measures for reformers
Elements Hazard Safety measures
Burner, flame and combustion quality
Ignition of an explosive atmosphere
Safety measures are specified in standards
Materials damage of the oven and of the reforming tubes
Detection of an increase of the flame temperature thanks to the measure of the temperature of the gases in the oven and of the temperature of the syngas at the outlet of the reformer. Appropriate measures are then triggered.
Formation of deposits in the exchangers
Composition of the flue gases not in compliance with the composition specified in the standards
Automatically adjustment of the ratio air / fuels, with an excess of air. This adjustment takes into account the composition and flow rates of the fuels.
Continuous measure of the oxygen content of the flue gases. When a minimum value set as a threshold is reached, an alarm is triggered and the installation is shut down.
Reforming tubes
Steam production unit
Formation of a leak point on a reforming tube because of its early ageing
Abnormal pressure increase
Measure of the remaining content of process gas in the syngas. If there is a leak in a reforming tube, this content would decrease.
When a minimum value set as a threshold is reached, appropriate measures are taken.
Use of a pressure relief device
Detection of an abnormal pressure increase thanks to the measure of the tank pressure and of the water level in the tank. If an abnormal value is detected on either of the two sensors, the installation is shut down.
Coverage by standards

ISO 16110-1 Safety

The grade of the produced hydrogen is specified in the following ISO:

ISO 14687-2 for hydrogen used in fuel cells

ISO 14687-3 for hydrogen used in stationary applications.
Once hydrogen has been produced in large scale from a centralized production site
(e.g. by steam methane reforming), it must be transported to end users or applications
(e.g. refuelling stations, filling centres...). First, hydrogen is conditioned as a compressed gas or as a liquid suited for bulk transport. Then hydrogen is shipped either by pipe or in transportable containers or trailers to a terminal where it may be further conditioned, stored, or transferred to a local distribution mode. This section focuses on the delivery of hydrogen by pipe.
1.1.4.1
Description
Hydrogen transport by pipelines has been used for many years for supply to very large consumers, such as refineries
(see Figure 5 an example of oxygen, nitrogen,
hydrogen and carbon monoxide pipeline network). Compressed hydrogen is fed in metallic pipelines 1 , 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.
1 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 ist not resistant to high temperatures.

Hydrogen Pipelines
France
Zeebrugge
Dunkerque
Lille
Ghent
Mons
Maubeuge
Rotterdam Germany
Dordrecht
Netherlands
Rheinberg
Duisburg
Antwerp
Krefeld
Genk
Marl
Dortmund
Herne
Düsseldorf
Brussels
Belgium
Charleroi
Liège
Geelen
Leverkussen
12 networks worldwide
F/Be/NL: 810 km (100 bar)
Germany : 240 km (200 bar)
Figure 5: Hydrogen pipeline network of Air Liquide in Northern Europe (Reference: Air Liquide)
References:
 European Industrial Gases Association, 2004, “Hydrogen Transportation
Pipelines”, IGC Doc 121/04/E

Website of Air Liquide

Biennal Report on Hydrogen Safety, June 2007

Website of the US Department of Energy Hydrogen and Fuel Cells Program: http://www.hydrogen.energy.gov/h2a_delivery.html

1.1.4.2
Safety measures and coverage by standards and certification
The main hazards and the associated safety measures are:
Table 2: Safety measures for pipes
Hazard Safety measures
Hydrogen compatible materials should be chosen. Rupture of pipes and fittings because of hydrogen embrittlement
Corrosion 2 for underground piping
Rupture of the pipe material due to lightning strikes or ground fault conditions
Rupture due to external forces
Hazards specific to underground piping
Piping must be externally coated to an approved specification, to protect against soil corrosion .
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
Piping should not be exposed to external forces which can cause a failure or dangerous situation.
It is preferable to have no flanged or other mechanical joints underground. Only gaseous hydrogen pipes with welded joints may be buried.
Note: if underground piping is run in a jacket pipe, risk of release of hydrogen from the jacket pipe due to a leak on the hydrogen pipe shall be considered for preventing explosions and fire hazards at jacket pipe outlet.
2
There is a difference in electric potential between the pipe and the soil which sets up an electro-chemical cell.

The main cause of pipe rupture is attack by external operation (e.g. when a mechanical digger knocks on a pipe).
Note: as always for piping, pipelines shall be pressure-tested to 110% of the design pressure proven gas-tight prior to the first use with hydrogen. Pressure testing can be done using either a helium-nitrogen mixture containing at least 5 vol. % helium (preferred method), helium or nitrogen. If helium or a helium-nitrogen mixture is used, leak testing can be done at the same time with the same gas. If nitrogen is used, the system shall also be leak-tested at 100% of design pressure with hydrogen.
References:
 European Industrial Gases Association, 2004, “Hydrogen Transportation
Pipelines”, IGC Doc 121/04/E

Biennal Report on Hydrogen Safety, June 2007
Coverage by standards
Design, fabrication, inspection, examination and testing of hydrogen transportation pipelines shall be in accordance with national or international standards, such as
ASME B31.3 and B31.8.
1.1.5.1
Description
For consumptions of up to a 200 Nm 3 /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 .

Figure 6: Examples of compressed hydrogen tube trailers
(Source: Air Liquide)

A typical tube trailer has a capacity of 400 kg. This capacity can be largely increased by use of composite materials.
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 time is challenging because of its rapid evaporation in case of parasitic heat input. Tankers are insulated, and they may have large capacities exceeding 60 000L.
Figure 7: Liquid hydrogen tanker
(Source : Air Liquide)
References:

Website of the US Department of Energy Hydrogen and Fuel Cells Program: http://www.hydrogen.energy.gov/h2a_delivery.html

Biennal Report on Hydrogen Safety, June 2007

1.1.5.2
Safety measures and coverage by standards and certification
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. o Safety relief valves start to open at their set pressure. They re-set when the pressure is at 90% of the set pressure. o 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.
Source : Extract from “Road Vehicle Emergency and Recovery, IGC Doc 81/06/E,
Revision of Doc 81/01, European Industrial Gases Association AISBL ”
Reference:

Road Vehicle Emergency and Recovery, IGC Doc 81/06/E, Revision of Doc
81/01, European Industrial Gases Association AISBL
Coverage by standards:

Bundles (cylinder packs) ISO 10961

Trailers EN 13807
The ADR is a European Agreement concerning the International Carriage of
Dangerous Goods by Road; it includes important information on requirements and approval processes. See additional information in section Ошибка! Источник ссылки не найден.
.
Note: the United Nations Economic and Social Council's Committee of Experts have developed recommandations on the transport of dangerous goods. For additional information on these UN model regulations, http://www.unece.org/trans/danger/publi/unrec/rev13/13nature_e.html see:

1.1.6.1.1 Description of hydrogen supply systems
Hydrogen installations are usually designed to perform two functions: (i) storage of hydrogen delivered by road and (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 switch-over 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.
Using two hydrogen containers to provide a continuous hydrogen supply facilitates logistics as a lapse of time is provided for exchanging the depleted container against a full one.
Figure 8: Block diagram for hydrogen supply from two hydrogen trailers
(Source: Air Liquide)

2. Product transfer : 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 9: Flow diagram for gas transfer
(Hydrogen Vessels (GH2 – 45 bar) at Air Liquide Germany, Wolfgang Otte,
Paris, 2007)

1.1.6.1.2 Hazards and safety measures
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
1.1.6.2
Coverage by standards and certification

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

For buffers: ISO 15399