Energetic Uses of Hydrogen

5.2.4.1 Hydrogen in Private Cars

We now consider specific safety risks in the hydrogen-powered vehicle (e.g. private car), by examining onboard hydrogen systems failures that might lead to hazardous conditions, in both normal operation and during a collision. In general the hydrogen vehicle has relatively few potential hazards compared to other vehicle systems. There are no toxic chemicals, acids, and so on that could harm the environment. A study carried out by [185, DTI (2003)] concluded that the only potential hazard to hydrogen-fuelled vehicle is due to the hydrogen itself. Most of the time a large amounts of hydrogen is available in the storage tank. The study therefore was limited to one issue, i.e. the failure modes which could lead to a release of hydrogen from the hydrogen tank and the piping system.

The study considered a hydrogen private car (e.g. BMW 735i) where hydrogen is stored in liquid form (LH2) in a cryo-tank at a temperature of -253°C, and at a pressure of about 0.5 MPa. Similar to the previous plant, the scenarios for the hydrogen car are given in Table 5-4.

Table 5-4 List of accident scenarios for the onboard LH2 storage in private car

Scena rios

Undesired events

Inner diameter (mm)

Release Direction

Type of Bund Surface

Discharge Data

Type

Phase

Tank

Pipe

Hole

Flowrate (kg/s) or mass (kg)

Duration (s, or inst)

A

Tank rupture

400

-

-

-

N/A

6

Inst.

B

Tank leak

Liquid

400

-

12.7

Down

N/A

3.4

1.8

C

Relieve valve

Vapor

400

12.7

5.08

Vertical

N/A

0.1

79.5

D

rupture disc

Vapor

400

12.7

12.7

Vertical

N/A

0.2

40.4

E

Line rupture

Vapor

400

12.7

12.7

Vertical

N/A

0.2

33.9

F

Line rupture

Liquid

400

12.7

12.7

Vertical

N/A

0.2

29.9

Table 5-5 List of accident scenarios considered for the L

H2 storage at the CHP plant

Table 5-5 List of accident scenarios considered for the L

H2 storage at the CHP plant

Scena rios

Undesired events

Inner diameter (mm)

Release Direction

Type of Bund Surface

Discharge Data

Type

Phase

Tank

Pipe

Hole

Flowrate (kg/s) or mass (kg)

Duration (s or inst)

A

Tank rupture

Liquid

3100

-

-

-

N/A

4200

inst.

B

Tank leak

Liquid

3100

-

76.2

Down

N/A

30.4

138.3

C

Relief valve

Vapor

3100

50.8

50.8

Vertical

N/A

3.5

1211.9

D

Rupture disc

Vapor

3100

50.8

50.8

Vertical

N/A

3.6

1173

E

Line rupture

Vapor

3100

50.8

50.8

Vertical

N/A

4.2

1010.6

F

Line rupture

Liquid

3100

76.2

76.2

Vertical

N/A

10.9

387.2

5.2.4.2 Hydrogen for Household Applications

As described in section 3.7, the safety evaluation of hydrogen for household applications, i.e. fuel cells-combined heat and power (FC-CHP) plant was focused on the LH2 storage and its environment. The LH2 storage marks the largest contribution to the overall risk. The LH2 tank has a capacity of 66.3 m3 (about 4200 kg of LH2). The list of accident scenarios considered for the LH2 storages at the CHP plant is given in Table 5-5.

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