H2Tech - Q4 2021 - 32

GREEN HYDROGEN PRODUCTION
make-up water to the bottom water basin
of the scrubber. It is from the gas scrubber
that feed water is mixed with the lye
and then routed to the electrolyzer.
H2
electrolyzer may contain residual oxygen.
The H2
an appropriate pressure and then passed
through a deoxidizer, a small catalytic reactor
that combines any remaining oxygen
with the H2
The wet H2
dehydration unit, where the water is removed
to generate dry H2
suited to both solar and onshore wind
gas produced from the alkaline
gas is first compressed to
to produce water vapor.
gas is then transferred to a
at the required
product specification, after which it is
sent to storage for export.
The intermittency of renewable
power
generation. The challenge:
The plant utilizes renewable energy-
provided by a 70-MW onsite solar photovoltaic
(PV) array and a 96-MW onsite
wind farm-to generate green H2
. The
plant is to be built in a coastal region of
Western Australia, a location that is wellpower
generation, as the climate in this
region enjoys extended periods of sunshine
and land and sea breezes.
However, both sources of renewable
energy are intermittent and fluctuate
both on a daily and seasonal basis. Solar
PV generates power only during the daytime,
depending on the amount of solar
irradiance that reaches the panels, which
is impacted by cloud cover (FIG. 4). The
power generated by wind turbines-provided
they are oriented to the correct
wind direction-is largely dependent on
wind speeds, which vary greatly throughout
the day, as shown in FIG. 5.
Therefore, it will be difficult to guarantee
sufficient, steady, reliable and continuous
power to satisfy the electricity
demand from the electrolyzer unit from
either or both sources. A reliable backup
supply of electricity is necessary to make
up for any drop in solar and wind power.
The approach: The Stage 1 plant requires
60 MW of electrolyzer capacity,
with about 20% more power to generate
25 metric tpd of H2
gas. To deal with the
intermittency of the renewable powergenerating
assets onsite, the facility is
furnished with a connection to the electricity
grid, as shown in FIG. 6. Through
this connection, any deficiency in renewable
energy supply can be topped up by
importing green power from the grid to
maintain a steady power supply to the
electrolyzers and the entire facility.
The green grid connection can also be
used to export surplus power that is generated
during the day, which provides additional
revenue and can also be used to
help mitigate against the risk of low H2
demand or low market prices.
In addition, a 6-MWhr battery storage
system is provided to attenuate/buffer
the renewable power that is supplied to
the facility; the system can hold enough
power to maintain H2
production in the
plant for about 5 min. The battery storage
system would also enable a controlled
ramp-up and ramp-down of H2
production,
a safe shutdown of the plant in the
event of a total power failure, and the
potential to increase production during
periods of low onsite power generation.
FIG. 4. The 5-d irradiance data from Fulcrum 3D sodar at the Arrowsmith site.
Wastewater management. The challenge:
The project has access to goodquality
water from a local aquifer that
requires minimal treatment to transform
it into the demineralized water required
for the electrolyzer units. To generate 25
metric tpd of H2
, some 537 metric tpd of
FIG. 5. The 5-d wind speed and direction data from Fulcrum 3D Sodar at the Arrowsmith site.
aquifer water is required-about half of
that amount is converted to demineralized
water that is fed to the electrolyzers, while
the other half is discarded as reject water
from the WTP. The design from the concept
stage routed the reject water to evaporation
ponds, resulting in a pond area of
around 400 m2
to dispose of the water in
this part of Western Australia (FIG. 7).
Considering that freshwater is a scarce
and valuable resource around the world,
the amount of reject water and the area
of land required for the evaporation pond
are both opportunities for design optimization.
In addition, the roadmap plans to
expand the facility to produce 300 metric
tpd of H2
-this will likely require
FIG. 6. Arrowsmith Hydrogen Plant schematic.
32 Q4 2021 | H2-Tech.com
seawater desalination, an energy-hungry
process, to provide feed water. Therefore,
maximizing the amount of water utilized
from the local aquifer would pay rich dividends
down the line.

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