System Description

The station is designed to provide hydrogen as fuel for transportation purposes both in liquid (LH2) and compressed gaseous (CGH2) form. The CGH2 is required for a BVG city bus operated on a regular route in Berlin. On the study visit the station was not used to deliver LH2 to any vehicle, and all the hydrogen was converted into CGH2. The station stores hydrogen in liquid (LH2) form (-253°C, 0.8 MPa), and delivers it in the form of CGH2 to a hydrogen storage at vehicles at 25 MPa and 15 °C [228].

Biohydrogen Diagram
Figure 3.10 Process flow diagram of a LCGH2 filling station

Fig. 3.10 shows the process flow diagram of the hydrogen filling station including all the major components: (1) A double walled super-insulated (cryogenic) tank, to store LH2 with a capacity of 12,000 litres (800 kg of LH2) at a temperature of -253°C and pressure of 0.8 MPa; (2) An ambient air evaporator, used to vaporize the liquid hydrogen to gaseous hydrogen by taking heat from the air; (3) A multi-stage diaphragm compressor, to raise the pressure of the gaseous hydrogen to three levels, i.e. 15 MPa, 20 MPa, and 35 MPa; (4) A tube trailer, used to store compressed gaseous hydrogen at three levels of pressure (15 MPa, 20 MPa, and 35 MPa), with a capacity of 60 kg; (5) A CGH2 dispenser, to deliver compressed gaseous hydrogen to hydrogen vehicles (at 35 MPa).

The figure shows that the station filling process begins with the bulk delivery of LH2. There is a dedicated lane around the station for LH2 tanker operation. The tanker will pull in to the station, park under the storage and distribution system, and connect its hoses to the LH2 double-walled vacuum storage tank (a Dewar vessel). The LH2 is stored in the Dewar at a temperature of -253°C, and pressure of about 0.8 MPa. When hydrogen is needed, it is drawn from the Dewar by gravity and passed through an ambient evaporator where it temperature increased to about -30°C [197, 228]. The cold hydrogen gas is stored in a small buffer storage tank. A multi-stage compressor is then applied to increase the pressure to three levels of pressure (i.e.15 MPa, 20 MPa, and 35 MPa) and store it in tubes of a trailer with a capacity of about 60 kg (680 Nm3) of hydrogen.

The LH2 storage has the largest hydrogen inventory compared to other equipment in the filling station. Therefore, the study focused on the LH2 storage where its risk may dominate the societal risk of the filling station.

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