H2Tech - Q1 2022 - 38

GREEN HYDROGEN PRODUCTION
The H2
purity requirement of 99.999
vol% has eliminated several compressor
options, such as lubricated reciprocating
compressors, due to the potential
for contamination of the H2
gas product.
Centrifugal and rotary-screw compressors
were considered unsuitable for the
operating ranges of low-pressure (LP)
and HP compressors due to the relatively
high compression ratio and low H2
flowrates.
In keeping with the production of
green H2
, compressors driven by electric
motors were selected over those with engines
or turbines powered by gas.
A limited pool of OEMs exists for
proven green H2 equipment (e.g., electrolyzers,
compressors and H2
liquefaction
packages) at this scale, which constrains
the supply chain in the current
active market. Early supplier engagement
is critical to the success of projects
such as this one. At the start of the project,
significant effort was therefore made
to build collaborative relationships with
OEMs-especially the electrolysis package
vendors-and identify preferred
suppliers to mitigate this supply chain
risk. Such an approach pays off enormously
in delivering safe and optimal
designs for green H2
production systems
at these novel scales.
For the H2
compression example, two
suppliers were eventually identified as
capable of meeting the LP compressor
duty requirement in a single non-lube reciprocating
compressor with five stages
of compression. One supplier was identified
for the HP compressor duty that
recommended a single-diaphragm compressor
with two stages of compression.
Process safety considerations of H2
facility are well
:
Challenges and approach. The hazards
presented in an H2
understood and documented within the
industrial gases sector. The electrolysis
and liquefaction processes primarily produce
three hazardous fluids: H2
and oxygen (O2
gas, LH2
) gas. Significant work
has been done by organizations (e.g., the
European Industrial Gases Association)
to develop operating and design standards
for use on such facilities.
H2
gas is highly flammable, with a
flammability envelope of between 4%
and 75% in air. Ignition energies are
also significantly lower compared to
light hydrocarbons. Together, these two
properties result in a high probability of
ignition on release. Immediate ignition
can lead to a jet fire, which burns with an
almost invisible flame (visibility is better
at night). This is potentially hazardous
since there is little visual warning to personnel
of an ignited leak.
Late ignition can result in an explosion
with a tendency towards detonation
in confined volumes. Due to the low molecular
weight of H2
, a release will rapidly
rise. This is particularly hazardous in
areas where the gas can accumulate, such
as under eaves or in roof spaces or other
confined areas.
LH2
to the very low temperatures at which it
must be stored. Leaks from piping or vessels
can lead to the formation of a large vapor
cloud with the potential for ignition.
O2
gas is a byproduct of the electrolysis
process-in this project it was vented to
the atmosphere. High concentrations of
O2
lead to enhanced combustion with
the potential for aggressive O2
fires.
A standard process safety manageFIG.
9. The best source of low-carbon H2 in different regions.5
ment framework was used during the
design stage to identify hazards, determine
the extent of the consequences, and
identify prevention and mitigation safeguards.
A hazard identification (HAZID)
process was undertaken to identify the
major accident hazards (MAHs) within
the facility. Each MAH was modeled using
the proprietary consequence modeling
packagea
. The results were used to
identify specific engineering safeguards
for inclusion in the design.
Two main preventative barriers were
identified for the H2
systems: leak prevention
and material selection for piping.
Regarding leak protection, the design
basis required that all piping be fully
welded as much as possible. H2
is an exFIG.
10. Cost estimates of blue and green H2
38 Q1 2022 | H2-Tech.com
production to 2050.
ceptionally small molecule, and leakage
through flanges and fittings is common.
Material selection for piping was also
has additional hazards relating
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