A hydrogen refueling station (HRS) is an infrastructure designed for filling a vehicle with hydrogen fuel. It can be part of a station for fossil fuel refueling or an independent infrastructure.
- A HRS is composed of a basic unit, or of a basic unit plus a production unit, if the hydrogen is produced on site.
- The basic unit includes as minimum a high-pressure storage system and one or more dispensers.
- If the H2 is produced on site or is delivered to the station at an intermediary pressure or in liquid state, the basic unit also requires an intermediary storage (based on gaseous or liquid hydrogen technology) and a compression system.
- Certain technical components are necessary for the construction of a hydrogen refueling station. For all refueling stations these include adequately sized storage facilities for hydrogen, compressors which bring the hydrogen to the desired gas pressure level, a precooling system, and dispensers for delivering the fuel. Refueling stations can be set up more quickly and less expensively by standardizing these components.
Hydrogen storage tanks
The storage tanks must hold enough hydrogen to meet customer demand. To this end hydrogen is stored in low-pressure tanks, currently at between 20 and 200 bar (in future up to 500 bar), for several days. If the hydrogen is delivered by compressed hydrogen gas trailer, this can be used on site as a low-pressure storage tank. The quantities to be stored are calculated on the basis of the number of anticipated refuelling operations per day and can be adapted with a modular expansion of the refuelling station.
Medium- and high-pressure storage tanks, with pressure stages of 200 to 450 bar and 800 to 1,000 bar respectively, are used to refuel the customer vehicle. The hydrogen from the low-pressure storage tank can be transferred via a high-pressure compressor to the high-pressure storage tank. The pressure there is high enough to refuel the vehicle. Another possibility is to use a medium-pressure storage tank. From there the customer’s vehicle tank can be filled until pressure balance is reached. To fill up the tank completely, refuelling can then either be continued from the high-pressure storage tank (cascade refuelling) or hydrogen from the medium-pressure storage tank can be compressed to the necessary pressure using a booster compressor.
A number of different compressors can be used to achieve the necessary compression. Customary types are piston, compressed air, diaphragm or ionic compressors, which are selected according to the design of the refuelling station (capacity utilisation, energy consumption, cost-effectiveness, etc.). Hydrogen compression is a way of overcoming the pressure difference between storage (from 50 to 200 bar) and refuelling (up to 1,000 bar). The refuelling process should not exceed the target time of three to five minutes.
Since the fuel cell in the vehicle is operated with pure hydrogen, it is important that no contamination with lubricants occurs during compression.
The SAE J2601 fuelling protocol, which covers hydrogen vehicle refuelling, aims to ensure that a vehicle’s hydrogen tank does not heat up above 85°C even during fast refuelling. Since hydrogen is compressed during refuelling, it heats up. Depending on ambient temperature, fuel delivery temperature and target pressure in the vehicle tank, precooling (normally) is necessary to stay in within the limits (overpressure/overheat) of the vehicle’s fuel storage system. For 700 bar refuelling hydrogen is generally precooled to –40°C (according to SAE J2601). Higher precooling temperatures are possible, but may lead to longer refuelling times.
The low temperature required is usually generated by means of a compression refrigerating machine and a suitable heat exchanger. Precooling adds complexity to the station and increases its energy consumption. Further optimisation of the process is currently an area of development.
In the case of a liquid hydrogen refuelling station, cryogenic hydrogen (LH2) is delivered and stored in a liquid tank. If the fuel cell electric vehicle is to be refuelled with gaseous hydrogen, liquid hydrogen is transferred via a liquid pump to an evaporator, from where it can be introduced directly into the vehicle without being cooled.
Refueling itself is carried out using the dispenser, a device or machine to pump liquid or gaseous fuels into the vehicle. The dispenser includes the fueling nozzle, which delivers the compressed hydrogen into the vehicle’s pressure tank. It is designed for the pressure of the hydrogen tank, i.e. 350 or 700 bar. Another important element is the user interface, which contains various displays showing pressure, fill level or measured quantity.
Finally, the hydrogen can be produced either locally at the refueling station or centrally in another location and then delivered. In the case of decentralised hydrogen production at the refueling station, the production concept has to be decided. The options are a reformer for producing hydrogen from natural gas (or biomethane) or an electrolyser for producing hydrogen from (renewable) electricity.