che_november-2024 - 23

700 bars for various applications,
including plant operations and onvehicle
systems.
* Stress and vibration. Any operational
stresses and vibrations a hydrogen
system encounters have the
potential to cause fitting connections
to work themselves loose and
cause leaks. Hydrogen fuel systems
must be able to withstand those
stresses and remain tightened and
leak-free.
* Safety. The use of hydrogen carries
numerous potential risks. Systems
must be designed to mitigate
threats related to gas leakage, temperature
increases, and hydrogen
embrittlement. In addition, the average
consumer must be able to safely
operate a refueling station.
*
Maintenance. It should also be
easy to remake leak-tight joints
when they need to be serviced for
any system, including at the production,
storage, transportation and
usage level.
These four performance parameters
cannot be sacrificed. Each
selected valve should provide leaktight
performance at connection,
shutoff and regulation points. System
designers should then specify
valves with the particular challenges
and
necessary operating conditions
of hydrogen applications top
of mind.
Those valves may include any of
the following types:
Hydrogen ball valves. Hydrogen
systems often contain ball valves,
which start and stop gas flows from
one direction to the next (Figure 3).
Proper hydrogen ball valves should
include wear-resistant stem-seal
designs. For example, it may make
sense to specify a trunnion-style
ball valve with a direct-load design,
which
provides
leak-tight
performance
each time it is activated and
shut off.
Another option is a bottom-loaded
stem design, which can be safer than
other valve designs, because such
valves are less likely to blow out their
stems. Hydrogen ball valves may
also offer two- or three-way functionality,
different mounting options, and
a range of flow coefficients to meet
varying system needs. Regardless
of the specific valve chosen, always
look for good compatibility with fittings
that are designed specifically
for hydrogen applications. A qualified
valve supplier can help guide
your selection.
Hydrogen needle valves. When
fluid flows require fine adjustments,
needle valves are often the answer
(Figure 4). However, other factors
influence whether needle valves are
right for specific hydrogen applications.
First, they are often made
completely out of metal, meaning it
takes significant force to open and
close them. The amount of force
necessary might eventually deform
the needle and seat, rendering it incapable
of operating properly and
presenting a potential safety issue.
Additionally, large air actuators are
typically used to open and close the
valves, which can take up to two
minutes to complete.
Given the above factors, it is evident
that hydrogen needle valves
must be made from the strongest
possible
steel.
High-quality 316
stainless steel, for example, resists
deformation over time and can
withstand the pressures exerted on
valves in hydrogen applications (usually
350-700 bars). The composition
of that steel is especially important
so it can better resist the challenges
related to hydrogen embrittlement
(see the sidebar for details).
Not all needle valves will have
FIGURE 3. Ball valves for hydrogen applications
should have highly wear-resistant stem seals
for safety
the required pressure rating to
handle common hydrogen applications,
so when selecting, be sure
to choose valves that are qualified
for elevated working pressures. In
addition, ensure the chosen neeCHEMICAL
ENGINEERING WWW.CHEMENGONLINE.COM
NOVEMBER 2024
FIGURE 4. Hydrogen needle valves should be made
from high-quality 316 stainless steel
FIGURE 5. Ball check valves are used to control
excess backflow in hydrogen compressors for
refueling systems
dle valves are compatible with any
other hydrogen-qualified components
used in the system.
Hydrogen check valves.
Finally,
check valves are essential to properly
functioning hydrogen compressors
in refueling systems (Figure 5).
For example, most check valves
use strain-hardened springs, which
can be unusually susceptible to hydrogen
embrittlement. In contrast,
using springs made from high-quality
316 stainless steel reduces the
chances of embrittlement weakening
the springs. Another challenge
is the often severe temperature and
pressure changes common to hydrogen
applications. These severe
changes can damage the elastomer
seals in valves. Ideally, most
hydrogen compressors would use
ball check valves over other nonspecific
ones.
Just like with the other two types
of valves, material integrity and
compatibility with other hydrogen
components are important for
check valves.
23
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