The GH storage

The high-pressure hydrogen tank of the plant stores the largest hydrogen inventory of 5000 Nm3 compared to other components. It may be the largest contributor to societal risk as assessed in this study. Therefore, the study is focused on the two horizontal cylindrical high-pressure hydrogen storages (Fig. 3.4) with an operating pressure of 3 MPa at ambient temperature. The tank is filled directly from the water electrolysis in the plant generated from the two low-pressure electrolyzers requiring subsequent compression of the product gases. The stored hydrogen in this plant is mainly used for energetic utilization, such as fuel cells and gas-fired heating boilers of calorific-value. Two types of fuel cell plants, i.e. alkaline and phosphoric acid were tested.

Biogas Isolation Valve
Figure 3.4 GH2 storage at the solar-hydrogen plant [215].

HP filing MP filling

Electrolysers ■ Compressors

P&ID legends:

PCV-20

PCV 16,17,19

V12-13

V-34

V20s

F1-3

HP filing MP filling

Electrolysers ■ Compressors

Rupture Disk

- Pressure control valve (Emergency shutdown valve)

- Pressure reducing regulator valves with external tap

- Remote operated (isolation) valves -Hand operated valves

- Check valve

- Drain valves

- Pressure safety valves

- Rupture disks -Three-way valves

- Filter

- Pressure indicators

- Pressure indicator alarm

- Pressure switch high

GH2 Tank I 2500 NmJ Capacity; 30 bar, 20°C

GH2 Tank I 2500 NmJ Capacity; 30 bar, 20°C

GH2 Tank II 2500 Nrrr' Capacity; 30 bar, 20°C

- Pressure control valve (Emergency shutdown valve)

- Pressure reducing regulator valves with external tap

- Remote operated (isolation) valves -Hand operated valves

- Check valve

- Drain valves

- Pressure safety valves

- Rupture disks -Three-way valves

- Filter

- Pressure indicators

- Pressure indicator alarm

- Pressure switch high

GH2 Tank II 2500 Nrrr' Capacity; 30 bar, 20°C

P&I DIAGRAM

GH2 Tank at H2 Production Plant

P'jsYICi. O. A.

,'."7" 1 "~h„t il,,™

Figure 3.5 Simplified P&I Diagram of the GH2 storage [119, 102].

Table 3-1 Most important capacities and dimensions of the GH2 storage

H2 Storage /lines

Dimension

Capacity

1. High-pressure vessel

2. Input line

3. Output line

Vuseful =50m3

50.8 mm (2 in) 50.8 mm (2 in)

2x2500 Nm3 (*) 30 bar (400 kg) 30 Nm3/h 30 Nm3/h

Source: Messer Griesheim GmbH, Linde AG; (*) m3 H2 at 15°C, and 1 bar (NTP)

Source: Messer Griesheim GmbH, Linde AG; (*) m3 H2 at 15°C, and 1 bar (NTP)

Fig. 3.5 shows a simplified piping and instrumentation diagram of the high-pressure storage. The tank is filled from electrolysers continuously during the day (e.g. 200 /year) through filling valve, V7 and V13. The filling process is stopped when the set point at the pressure control valve, PCV-19 is reached. Pressure indicator and alarms (PIA) are installed to measure and indicate pressure levels of the tank and its piping system. The tank PIAs are equipped with pressure switch or transmitter for remote controllers (e.g. alarm). If the operator fails to observe PIAs or to respond to the alarm the tank pressure increases rapidly and the tank is overfilled.

To protect against overpressure, each tank is equipped with two pressure safety valves (SVs) and a rupture disk (RD). One of the SVs is operated exchangeable at the relative pressure of 3.3 MPa. The SVs will automatically re-close if the tank pressure returns to the operating pressure. The rupture disks (RD-1 and RD-2) are provided in case the safety valves should fail. The ultimate overpressure protection of the tank is provided by stopping the filling line automatically. It is performed by a safety shut-off (PCV-20), which is actuated by PSH signal. The gas is withdrawn from the tank through withdrawal valve V12. The required output pressure is determined by setting pressure at the pressure control (i.e. high pressure=PCV-16, low pressure=PCV-17).

3.4 HYDROGEN STORAGE

The study focuses on liquid hydrogen (LH2) storage situated in the Vonburg-Ingolstadt-Refinery (RVI), Germany, as a representative example. The LH2 storage is used to store liquid hydrogen produced from the hydrogen liquefaction plant. The LH2 is delivered to the consumers (e.g. hydrogen filling station) through a LH2 tanker truck. The tank is directly filled from a liquefaction plant with daily capacity 4.4 ton LH2 per day, and presently is the largest hydrogen liquefaction plant in Germany [78].

Gas purification

Gas purification

Linde Liquefaction Gases
Figure 3.6 Process flow diagram of the liquefaction plant [78] 3.4.1 System description

The Linde liquefaction plant (Fig. 3.6) mainly consists of compressor units, Pressure Swing Adsorption (PSA) purification, liquefier, and LH2 tank. The hydrogen rich raw gas supplied from the RVI refinery has pressures varying between 0.9-1.4 MPa. The gas is then compressed to about 2.1 MPa, and is cleaned in PSA purification units. The gas is further purified by low temperature and liquefied into para-hydrogen [78].

The liquefaction process which is designed for a flow rate of 180 kg/h based on the Claude cycle. The necessary refrigeration is provided at three temperature levels using: LN2 (from 300K to 80K), expansion turbine (80K to 30K), and Joule Thomson (JT) valve (30K to 20K). The cooling down process from ambient to LN2 temperature levels is operated manually for about 5 hours. Once the LN2 temperature is reached the operating mode of 50% or 100% LH2 can be selected from the monitor screen, and the process control system starts automatically. The steady state liquefaction is achieved after a further 3 hours. Opening the JT valve and hence liquefaction capacity is controlled by the outlet temperature of the third turbine.

The liquid hydrogen is then stored in a horizontal vacuum insulated tank at -253°C having a capacity of 270,000 litres. The tank can store hydrogen for several weeks without significant vaporization [78]. The LH2 is transported to consumers by using an LH2 tanker truck, which is loaded in the filling station. The whole plant is operated and controlled by a central process control system (PCS).

Hydrogen Liquefaction Plant
Figure 3.7 Hydrogen liquefaction plant in Germany [78]
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