H2Tech - Q4 2021 - 45

HYDROGEN STORAGE
Long-duration H2
storage
in solution-mined salt caverns-Part 2
L. J. EVANS, Global Gas Group, Houston, Texas and T. SHAW, LK Energy, Houston, Texas
Part 1 of this article, published in the Q3 issue, discussed
the variety of methods available for storing H2
, the need for
dispatchable energy and the benefits of having a mix of storage
alternatives during seasonal events. The final segment of this
article series examines the environmental impacts and sustainability
of H2
storage, as well as opportunities for process
and facility integration.
Environmental considerations. Environmental, social, and
corporate governance (ESG) is an increasingly important aspect
of corporate strategies and investment decisions. The authors
have considered the environmental impacts and sustainability
of H2
energy storage (HES), the specifics of which are
dependent on the combustion generation technology chosen.
Air emissions. The only emission from the electrolyzer is
resulting from the splitting of the water molecule. Fuel
free O2
cells, likewise, do not have any emissions other than fugitive
water vapor. Combustion technologies are associated with
CO2
, NOX, and thermal emissions.
CO2. When running on 100% H2
combustion technology has no CO2
, an HES plant using a
emissions. If blending with
methane during ramp-up is required, then 10 vol%-15 vol%
methane may be consumed for 3 min-10 min per cold start.
CO2
(> 80 vol%) can lower CO2
reduction when cofiring with natural gas is nonlincontent
of 40%, cofueling with H2
ear. When paired with an existing gas-fired turbine, assuming
a maximum H2
the CO2
reduces
emissions by up to 20%. Repowering with high H2
emissions by 50%-100%.
NOX. Due to the high flame temperature of H2
sions guarantee for high-H2
can be reduced to 15 ppm NOX
, water injection
cooling may be required for combustion generation,
which increases the rate of NOX
fuels is > 25 ppm NOX
trols. The primary impact of higher NOX
ditional capital and operating costs.
Thermal emissions. H2
formation. Typically, emis,
but this
with advanced emissions conformation
is the adburns
at a substantially higher
flame temperature than natural gas. As a result, ambient exhaust
temperature is higher than a natural gas plant. Potential
impacts are site specific, but rarely adverse, and can be mitigated
by waste heat recovery and/or exhaust cooling.
Water. Water is consumed during both charging and discharging.
Demineralized water is required for both electrolysis
and generation, so an HES facility will include a reverse osmosis
(RO) water treatment facility. The volume and composition
of waste brine and solids rejected during water treatment
will be site-specific and dependent on source water quality.
A HES facility utilizing fuel cells for the electrical generation
cycle can be constructed with a closed-loop water system, where
water is converted to H2
cell, where H2
combines with atmospheric O2
gas and then passed through the fuel
to form water,
which is then recovered and returned to the electrolyzer. Water
requirements are limited to makeup water for water vapor losses.
TABLE 6 shows estimated water requirements for varying
sizes of utility-scale, air-cooled gas turbines in the western U.S.,
paired with PEM electrolysis and running simple cycle with water
injection cooling. Recovery of water from the combustion
cycle by condensing the emitted steam has not been fully investigated,
so these estimates are maximum values.
Land use. The footprint of an HES utilizing salt cavern storage
is generally determined by the salt cavern size and spacing.
Surface facilities may occupy 5-50 acres (2-20.2 hectares), depending
on technology choices and building and safety codes.
Commercial availability and equipment supply chain.
Each element of an HES system utilizes proven, financeable
technologies, but the technologies may or may not have been
deployed at a utility scale, with purity H2
and/or integrated
at commercial scale. The authors are not aware of any other
compressed air energy project examples where combustion or
fuel cell technologies have been directly connected to salt cavern
storage. Consequently, the authors believe that opportunities
exist for process and facility integration to reduce costs
and/or improve efficiency. TABLE 7 summarizes significant integrated
HES projects that are proposed, as well as completed
demonstration projects.
Electrolysis. Electrolysis has been used for sourcing H2
TABLE 6. Water consumption by power output size
Output capacity, MWe
Process
Units
Electrolysis Gpm
l/min
Generation Gpm
l/min
Total
acre-ft/yr
m3
/yr
47.3
24
91
57
216
41.2
50,819
94.4
48
182
114
432
82.4
101,638
141.6
72
272
171
647
123.6
188.8
96
63
228
863
164.8
152,458 203,277
236
120
454
285
1,079
285
351,542
H2Tech | Q4 2021 45
at industrial
scale since before World War 2. Like batteries, the core technology
is mature, but recent innovations in new materials have
H2Tech - Q4 2021

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