The LH Storage

The liquid hydrogen (LH2) storage system is a cryogenic, double wall type, and vacuum super-insulated tank. It consists of an inner vessel of cryogenic chromium-nickel steel to hold liquid hydrogen at a temperature of -253°C and pressure of 0.8 MPa, and a supporting outer vessel of carbon steel. The space between the inner and the outer vessels is under vacuum and super-insulated with perlite. Fig. 3.11 shows a simplified piping and instrumentation diagram (P&ID) of the LH2 tank installed at the station. The LH2 tank mainly consists of following components: filling system, withdrawal parts, pressure building circuits, safety devices, instrumentation and control, and vacuum system.










- Pressure build-up regulator

- Pressure (control) relief valve

- Economizer

- Liquid withdrawal valve to evaporator

- Filling regulator valve

- Liquid withdrawal valve to LH2 dispenser

- Hand operated valves

- Outer relief valve

- Pressure safety valves

- Pressure building coil

- Pressure indicator controller

- Pressure transmitter

- Level indicator

- Level switch high

- Level switch high low

- Vacuum valves


LH2 Tank for a LCGH2 Filling Station

Figure 3.11 Simplified P&I diagram of the LH2 tank at filling station[216, 223]

Table 3-3 The capacity and dimension of the LH2 storage at filling station




1. LH2 tank

Horizontal insulated vessel

V=12,000 liter (800 kg).

2. Liquid lines

Diameter of 50.8 mm (2 inch)*

3. Vapor lines

Diameter of 50.8 mm (2 inch)*

Source. Linde AG; (*)Estimated values

Source. Linde AG; (*)Estimated values

The tank is normally filled from a LH2 tanker truck through the hose coupling C/1, pressure control valve PCV-5 and isolation valve V-2. Valve V-1 is used to inject the liquid hydrogen into the top of the tank in order to keep the tank pressure constant during filling. The filling is carried out by two operators who observe level indicators (LI). The filling is stopped manually if the level indicator (LI) reaches a high level. In case of operator fails to observe the LI, the level switch LSHL (which is connected to LI) will activate the alarm. The ultimate overfilling protection is provided by stopping the truck valve (PCV-47) automatically. It is actuated by the LSH signal. The signal is provided by overfill detector if the full trycock (V-22) is open.

The required tank pressure (operating pressure 0.7 MPa) is maintained by a pressure building circuit (PBC) which is regulated by the pressure controller PCV-1. The pressure is produced by converting the liquid hydrogen into gas by a pressure build-up evaporator D. The pressure controller PCV-2 ensures that the gas flows from the top of the tank into the vent lines when the tank pressure is too high.

To protect the tanks and piping system against overpressure, the system is equipped with two pressure safety devices (SV-1 and SV-2) with one of them in operation and the other one in standby. One of the two safety valves is operated exchangeable at a relative pressure of 0.77 MPa (10% of the operating pressure). Additionally, the PCV-2 is used as the secondary pressure relief device. The operation of the PCV-2 is controlled by the PIC using signal input given by tank pressure (PT). The valve is open if the tank pressure reaches the set point and it closes again if the tank pressure drops below the set point.

The liquid product is withdrawn from the tank through connector L/11-1 and L/11-2. The L/11-2 is connected to an LH2 dispenser through a flexible vacuum insulated hose. The L/11-1 is connected to an evaporator to be converted into gaseous hydrogen, compressed, and then stored in the high-pressure tubes trailer (at a pressure of 25 MPa) which is connected to the CGH2 dispenser.

The actual level and pressure inside the tank is measured and displayed by level and pressure indicators, respectively. The level indicator LI is a differential pressure gauge showing the tank contents in kg (or m3 gas). The tank pressure gauge and level indicator are also equipped with limit-switch contacts or analog signals for remote transmission.

The tank vacuum jacket is protected against overpressure by an outer vessel relief device, RV/O. While the line relief valves are installed in the external tank and piping system at points where the liquid becomes trapped. Evacuation valves (1-9) are installed to draw vacuum within the tank and piping insulation space. The vacuum gauge tube, PE is a connection point for vacuum probe to measure vacuum in the tanks insulation space.

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