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Hydrogen Transport Techniques


In the future, when Hydrogen has grown to be an integrated part of the energy distribution, it will (may?) be necessary to transport and distribute Hydrogen in large scale from a centralized production site to the consumer. In the long run, the best and safest way may be by Hydrogen pipelines, which have been operated for many years in e.g. Germany, France, Benelux and the US. This would need the establishment of a European wide grid, which is very costly and not a real option in the short term perspective.

Besides by pipelines, Hydrogen can be transported in pressurized and/or liquid form using ships, railways or road tankers. This is most likely the short term solution. Here the low energy density per volume of Hydrogen is a problem making the transport and distribution ineffectively and costly. Therefore, it is likely that Hydrogen is transported under cryogenic conditions or at very high pressures (current pressure of 200 bar could be increased). Finally, hydrogen may be transported by using the technique of bonded hydrogen. Bridging compounds like ammonia or methanol are one mean. Other means are metal and liquid (complex) hydrides and adsorbed on carbon compounds. They might be safer methods to applicate, presently. However, storage pressure is not the only safety risk factor. For instance metal hydrides are more sensitive to heat or impact than Hydrogen gas.

As with the natural gas distribution, in the case of centralized production and distribution, it will also be necessary for the Hydrogen system to establish central storage systems for different reasons. This could be in certain geological underground formations or in man made storages using different means (pressure, cryogenic and others). By that except for the pipeline system a number of loading and unloading from e.g. the ship to a storage, the storage to a road tanker etc. are needed that are generally regarded critical from the safety point of view. Another future option is the decentralized production of hydrogen either by water electrolysis from renewable energy sources or by local conversion of natural gas. Local or remote sources of electricity or natural gas could be used. In both scenarios no physical transport of Hydrogen over longer distances would be needed.

Transport using pipelines

Even though hydrogen distributed in pipelines demands better/more tightness for the pipe material itself and for seals and fittings and rises specific materials compatibility issues, the procedure is well known and has been safely in use for many years in industrial areas (IskovH:2000) for local distribution, which mean lengths of more than 2000 km. However, this is still modest as compared to a complete national or even international network delivering energy for fuelling stations, house warming, and industrial needs, especially related to a financial comparison with the current electrical, natural gas or propane system.

Hydrogen’s growing importance and the requirement of serving mass will lead to a hydrogen network of pipelines in order to connect new large scale production sites with end users and applications. In the long run hydrogen will be directly delivered via pipelines to filling centres, fuelling stations, to fuel cells used in small-scale distributed power generation etc. Prior to this situation, decentralized hydrogen production will take advantage of the existing natural gas infrastructure. The pipeline grid will possibly make use of the existing natural gas infrastructure which will be adapted to hydrogen.

It must be pointed out that piping hydrogen is problematic due to the energy required for pumping and the low volumetric energy density of hydrogen, demanding higher flow rates which in turn lead to greater flow resistance. Consequently about 4.6 times more energy is required to move hydrogen through a pipeline than for natural gas and 10% of the energy is lost every 1000Km (SylvesterBradleyO:2003). The capacity of a given pipeline configuration to carry energy is somewhat lower when it carries hydrogen than when it carries natural gas. In a pipe of a given size and pressure, hydrogen flows about three times faster, but since it also contains about three times less energy per cubic foot, a comparable amount of energy gets through the pipe.

The fact that hydrogen may not be compatible with the current piping infrastructure due to brittleness of material, seals and the incompatibility of pump lubrication poses further problems.

If the use of hydrogen pipelines were to be expanded, possible embrittlement problems would have to be considered. Pipes and fittings can become brittle and crack as hydrogen diffuses into the metal of which they are made. The severity of this problem depends on the type of steel and weld used and the pressure in the pipeline. The technology is available to prevent embrittlement, but depending on the configuration being considered, distribution costs may be affected.

Smaller piping can be used for hydrogen than those used for natural gas, due to the higher pressure requirements, smaller molecule etc. For example, the 3/8” tube that is appropriate for fuelling a bus with hydrogen would only be big enough to fuel a car with natural gas, not a natural gas bus (CampbellK:2002). However, if considering utilizing a single design for both hydrogen and natural gas, natural gas provides the limiting diameter, but the pressures and material compatibility for hydrogen must be met. Compressors would generally have to be refitted with new seals and valves.


Campbell K. and Cohen J. (2002) Why hydrogen vehicle fueling is different than natural gas. Presented at the World NGV 2002: 8th International and 20th National Conference and Exhibition, Washington, D.C..(BibTeX)
Iskov H. (2000) (Safety aspects and authority approval of the use of hydrogen in vehicles (in Danish). Dansk Gasteknisk Center, Projektrapport 1763/98-0019.(BibTeX)
Sylvester-Bradley O. (2003) Can the Hydrogen economy provide a sustainable future? Published on the website

Transport of gaseous hydrogen

Road transport of gaseous hydrogen is presently carried out using trucks with steel cylinders of up to 90 litres at 200 – 250 bar pressure or large seamless cylinders called “tubes” of up to 3000 litres at 200 – 250 bar. For transport in larger scale pressure of up to 500-600 bars or even higher may be employed. A 40 tons truck delivers about 26 tons gasoline to a conventional gasoline filling station. A 40 ton truck carrying compressed hydrogen can deliver only 400 kilograms [PFL] , because of the weight of the 200 bar pressure vessels.

Compression of hydrogen is carried out in the same way as for natural gas. It is sometimes even possible to use the same compressors, as long as the appropriate gaskets (e.g. Teflon) are used and provided the compressed gas can be guaranteed to be oil free. (ZittelW:1996) Depending on the desired use, hydrogen must be either compressed or liquefied. In most cases, however, high-pressure gaseous hydrogen is preferred over liquid hydrogen.


Zittel W., Wurster R. and B{\"o}lkow L. (1996) Hydrogen in the Energy Sector. T{\"U}V S{\"U}D Industrie Service GmbH {\tt}.(BibTeX)
!!! Transport of liquid hydrogen In order to reduce the volume required to store a useful amount of hydrogen - particularly for vehicles - liquefaction may be employed. Since hydrogen does not liquefy until it reaches ÷253°C (20 degrees above absolute zero), the process is both time consuming and energy demanding. Critical temperature for hydrogen is T=-240°C. This is the upper limit for liquefaction, at higher temperatures it is indeed impossible. T=-253°C is the equilibrium temperature at p=1bara. The advantage of liquid hydrogen is its high energy/mass ratio, three times that of gasoline. It is the most energy dense fuel in use (excluding nuclear fuels), which is why it is employed in all space programmes. However, energy/volume ratio remains a challenge. Liquid hydrogen is difficult to store over a long period (product loss by vaporisation), and the insulated tank required may be large and bulky. An illustration comparing energy densities between gasoline, diesel and hydrogen is shown in figure 1 below.

Liquid hydrogen road transport is carried out using trucks which can exceed a capacity of 60000 litres. Delivery is achieved either in vacuum insulated containers or by transferring the product to stationary vessels depending on the required quantities. In the USA there are several pipelines for liquid hydrogen with lengths of up to 40 km iii. The intercontinental transport of hydrogen will probably be carried out in liquid form using ships. For this purpose, specialized ships with appropriate tanks and port facilities are being designed. A realization of these ideas will however not take place until the trade in hydrogen reaches an appropriately large scale.

Transport in compound materials

To be included in later version

Gaseous Hydrogen refuelling stations


Several demonstration projects involving hydrogen refuelling stations are in operation. Examples from Europe are the CUTE and HyFleet:CUTE projects, ECTOS project and the CEP Berlin project. In the large European demonstration project, CUTE, 30 hydrogen operated fuel cell buses have been test-driven in 9 European cities. Hydrogen refueling stations have also been located in these 9 cities. The following descriptions and technology examples from hydrogen refuelling stations are mainly based on such demonstration projects as the CUTE, ECTOS and the CEP Berlin project.

Today's hydrogen gaseous stations are usually based on a few main components:

Hydrogen on site production or supply by pipeline or truck delivery

  • Purification/Drying in case of on-site production (often included in the production unit)
  • Compression
  • Storage and gas distribution
  • Hydrogen dispenser, including station/vehicle interface

A 3D drawing illustrating the main system components at the refuelling station at Iceland in the ECTOS project is illustrated in figure 1.

Below 2 hydrogen refuelling stations from the CUTE project are described.

CUTE station in Hamburg

The concept in Hamburg is illustrated below in figure 2. At the Hamburg station hydrogen is produced on-site by electrolysis using electricity

The filling station and production facilities are located at HOCHBAHN's bus depot in Hamburg Hummelsbüttel. Using electricity from the grid and combining this with the production from certified green electricity for the hydrogen production on-site is fulfilling all goals of ecology and sustainability. A pressurised electrolyser (15 bar) produces high purity hydrogen with high efficiency which is then compressed to 450 bar and stored in on-site storage tanks. Busses can be filled up with 40 kg of hydrogen in 10 minutes which enables them to operate up to a range of 250 -300 km.

CUTE station in Madrid

At the station in Madrid there are two options for hydrogen supply: on-site production by natural gas reforming and gaseous hydrogen.delivered by truck. The concept is illustrated in figure 3.

Hydrogen is delivered by 200 bar by tube trailers. Each one of them contains 3960 Nm3, composed of 264 small cylinders (85 liters) with hydrogen compatible with fuel cell requirements. Gas compression from these tube trailers to the bus is done by a water cooled membrane compressor. In Madrid Hydrogen is also produced on-site by a natural gas steam reforming process. An example of a principal sketch of a refuelling station concept downstream the production or supply unit is shown in figure 4.


The produced hydrogen, after being dried and purified, is compressed to about 450 bar (typical for the CUTE stations). The compressor(s) are usually located within an enclosure.

Buffer storage

Hydrogen is accumulated in high-pressure buffer vessels for fast transfer by pressure difference to the vehicle tank.. In order to minimize compression energy, the buffer is made up of multiple storage banks at different pressures, with the gas being taken first from the lower pressure bank (this pressure being sufficient to transfer product to the vehicle storage at initially low pressure) and then successively from pressure banks of increasing pressure. This is referred to as cascade refuelling further described hereafter. Maximum buffer storage pressure of 440 bar is typically required to refuell vehicles with 350 bar storage, in order to account for the temperature increase in the vehicle storage due to the fast filling. 700 bar refuelling requires 880 bar buffer storage.


The description below for the refuelling system is based on cascade filling and high pressure storage. There may also be other alternatives. The Fuel Gas Dispenser is usually a "stand-alone" unit, which provides the mechanical interface between the hydrogen fuel station storage tanks and the vehicle, together with safety features and metering equipment. The dispenser consists of a small enclosure where regulation and control valves are located. The principle of cascade filling can be explained for a 3 cascades concept as follows: The vehicles will start to fill from the low pressure bank. When the pressure in storage tank and vehicle tank is balanced, the filling will automatically continue from the next cascade, medium pressure bank. Finally, the filling will be completed by topping up the vehicle tanks from the high pressure bank. This process is usually fully automatic. A two stage cascade filling system combined with a booster compressor, or a multiple stage cascade filling system with more than three pressure banks are other options. This is to ensure that the on-board vehicle storage tank reaches the appropriate fill pressure within the required time. The compressed gas hydrogen dispenser usually has a vent stack line to the atmosphere.

Purging system

Inert gas purging systems, which can be initiated automatically or manually are important ancillary parts of the filling station. Inert gas purging systems may be used during start up and shutdown and in emergency situations.


Future hydrogen filling stations, including the Hydrogen production unit, may be fully automated and can be unattended, with remote supervision.. In case of deviations from normal operation conditions, the system is designed so that it will shut down to safe conditions automatically. Shutdown can also be initiated by pressing emergency buttons at the filling station area or from a remote location. In the CUTE project , the stations were designed for refuelling of 3 buses per day, which corresponds to a production capacity of 60 Nm3/h. Most stations in demonstration projects are only able to refuel a few vehicles (buses or cars) per day, and there is still a long way to go to achieve the same capacity as for petrol and gasoline stations. The reasons are challenges related to storage capacity (available area and volume), safety (high pressures) and the requirement for short refuelling durations. For overnight refuelling the technical requirements are less challenging. Most existing hydrogen refuelling stations are part of demonstration projects, and, so far, all require that the users receive proper education and training with regard to the safety related properties of hydrogen and the vehicle refuelling process. The refuelling technology is new and not fully mature, very high storage pressures are necessary to obtain the desired autonomy, and gaseous fuels still are quite uncommon in most countries. However, experience from the demonstration projects will allow improve the technology, as well as the public’s “familiarity” with new types of fuels.

Hydrogen used in clean vehicles running with a fuel cell or an internal combustion engine can be stored on board in liquid form at – 253°C at a pressure between one and ten bar. This type of storage allows a high energy density. It is then possible to store about 11 kg of hydrogen in a total storage of 75 kg and to use free form shapes (not only cylindrical) in the last generations of tanks made by Air Liquide.

This storage mode involves a liquid distribution network from the hydrogen liquefaction plants to the on board tanks with tube trailers of 45 000 litres capacity (about 3 tons of hydrogen). Liquid hydrogen is delivered to onsite storage vessels (buried or above ground), and then distributed to the vehicles at the hydrogen refuelling station, either by pressure difference or by the mean of a liquid hydrogen circulation pump.

When hydrogen is transferred by pressure difference, it is necessary to pressurize the source tank without heating in order to put the hydrogen in a subcooled state, allowing to avoid product vaporization in the transfer lines. Therefore, in case of a large source tank, this transfer mode involves the consumption of pressurization gas to make the transfer because the tank has to be depressurised between each transfer to avoid temperature increase of the hydrogen. This drawback can be managed by installing a buffer tank dedicated to pressurization between the source tank and the vehicle. In this case, filling of this tank is made at low pressure between two vehicle refillings, and only the buffer tank is pressurized to make the transfer.

The other transfer method of cryogenic liquid is to install a transfer pump, which allows circulation of liquid and subcooling. This method allows to fill the vehicle tanks without having to significantly increase the pressure of the source tank. The drawback is that a machine has to be used. This equipment transfers heat to the fluid and must be periodically inspected.

With the two methods, during transfer, a significant percentage of liquid hydrogen is used to cool down (or to compensate the heat losses of the lines) the lines and on board tank. This liquid hydrogen is therefore evaporated and sent back to the station through the vehicle connection. This hydrogen can be either reliquefied, vented to the atmosphere or compressed and sent to a compressed gaseous storage to be further used in a compressed gaseous refuelling station.

Those two methods are currently used in liquid Hydrogen stations in demonstration projects. The choice between the two technologies is based on the following criteria :

  • Maintenance cost
  • Number of fillings per day
  • Installation costs

Safety Challenges

The safety challenges result not only from the implementation of hydrogen technology for use directly by the public in a non-industrial context and for a completely new application. It lies also in the demanding performance and cost targets imposed by the applications leading to:

  • the excursion to new domains of service conditions (e.g. 700 bar, 85°C.)
  • the introduction of new physical processes (e.g. Hydride storage, fast filling.)
  • the use of new materials (e.g. composite materials.)

The safety challenge is hence two-fold:

1. Address the known risks (e.g. H2 leak) in a way that is compatible with the operation of a public fuelling station: the conventional methods used by industry (large clearance distances, personnel protective equipment…) are not easily applicable here; 2. Discover and address all the new risk factors brought in by the new elements above and their combination.

The fact that multiple actors are involved (cylinder and accessory manufacturers, vehicle manufacturers, refuelling station designers and operators, industrial gas companies...) further underlines this challenge.

More specifically the challenges include:

  • the reliability/safety of the 350 - 700 bar vehicle connection
  • ensuring the user’s safety despite his presence in an area normally classified as hazardous according to industry standards
  • perform the filling function well and safely, i.e. fill quickly to 100% exactly inside the safe operating limits, through correct management of the heat generated by the fast filling process
  • secure/safeguard the user( ensure safety despite limited knowledge and training and his/her potential “impatience”)

Prior to generalization/public use of such stations, further work is needed to

  • fully validate critical dispenser components, such as the fuelling nozzles, the hose and the break-away coupling
  • enhance prevention of leaks and potential ignition

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