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Liquid Hydrogen Refuelling Stations

Hydrogen used in clean vehicles running with a fuel cell or an internal combustion engine can be stored on board in liquid form at 253C 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

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Page last modified on December 19, 2008, at 11:06 AM