Established Methods Based on Compression and Cryogenics - Hydrogen Generation, Storage, and Utilization - page 79

TABLE 5.1 Hydrogen Compressibility Factor ( Z ) at 20°C and Corresponding
Volumetric Capacity

ρ V [4]

′

P (MPa) 0.1013 5 10 20 30 35 40 50 70 100

Z 1 1.032 1.065 1.132 1.201 1.236 1.272 1.344 1.489 1.702

m H (kg) in
150-L
tank)

0.0126 0.603 1.17 2.20 3.11 3.52 3.91 4.63 5.85 7.31

0.084 4.02 7.79 14.65 20.71 23.48 26.08 30.85 38.98 48.72

ρ V (g·L − 1 ) ′

tank at different compression pressure. The corresponding Z -factor is also
given in Table 5.1 [3]. For a standard 150-L compression tank, only when
the pressure increases to more than 50 MPa can the amount of hydrogen
stored in the compressed gas tank meet the requirement by DOE.
The gravimetric capacity can be expressed as

1 1

′ =

ρ M = . (5.10)

1 + m / m 1 + m ZRT MPV /

tank H tank tank

The mass of hydrogen m H stored in standard tank is calculated and listed
in Table 5.1. Clearly, the gravimetric capacity is determined by the mass of
the compressed tank. To meet the DOE's 2017 target, the mass of the tank
m tank ≤ 100.5 kg if the hydrogen can be compressed at 70 MPa.
Compressed hydrogen is stored in thick-walled tanks made of high strength
materials to ensure durability and safety. The standard compressed tanks use
pressure of 10-20 MPa, and are usually made of heavy steel- or aluminum-
lined steel. They cannot hold enough hydrogen for onboard applications, and
have a significantly low gravimetric and volumetric capacity (see Table 5.1).
The current trend to replace the standard gas cylinders is to use lightweight
composite fiber tanks. The state-of-art advanced lightweight storage system
is based on the designed philosophy of TriShield™ cylinder (QUANTUM
Technologies WorldWide, Inc.) as shown in Figure 5.3. The system is com-
prised of a seamless, one-piece, permeation-resistant, cross-linked ultra-high
molecular weight polymer liner that is overwrapped with multiple layers of
carbon fiber/epoxy laminate and a proprietary external protective layer for
impact resistance. Currently, QUANTUM has a commercial 129-L light-
weight H 2 cylinder working under 70 MPa. The weight of the cylinder is
92 kg, and stored useful hydrogen is 5 kg [6].
Besides the hydrogen content, another critical issue associated with high
pressure hydrogen storage is the compression. To compress hydrogen requires