POWER October 2021 - 38

HYDROGEN
Environmental and Permitting
Considerations for Decarbonizing
with Hydrogen
Many experts believe hydrogen will play a key role in the effort to decarbonize the
world's energy supply. However, current hydrogen production methods release a lot of
carbon dioxide, and carbon capture technology comes with its own complications and
added costs. Burning hydrogen in gas turbines also raises NOx emission concerns,
so there are still obstacles to overcome before hydrogen can fulfill its promise.
Tom Rolfson, PE and
Steven Babler
ydrogen is the most abundant
substance in the known universe.
It has been studied intensely and
used industrially-from agriculture to
rocket fuel-for decades. It's the smallest,
lightest
element in the periodic
table, and has both one of the highest
gravimetric energy densities and lowest
volumetric energy densities of gaseous
fuels. In short, hydrogen is, scientifically,
a well-understood element.
Despite this history and the global interest
in hydrogen as a method to help
decarbonize the power generation sector,
the use of hydrogen as an electric
power generation fuel source remains in
its infancy. The notion of using hydrogen
to decarbonize is multifaceted, but the
motivation is clear-the combustion of
pure hydrogen results in zero emissions
of carbon dioxide (CO2
). That said, there
are a variety of environmental considerations
associated with both hydrogen
production and hydrogen combustion
for power generation that necessitate
further exploration.
Hydrogen Production
Hydrogen can be produced by several
methods, categorized by different colors.
In the power generation industry, the
most applicable production methods are
steam methane reforming (SMR, grey
hydrogen), SMR with carbon capture and
sequestration (CCS, blue hydrogen), and
electrolysis of water using renewable
electricity (green hydrogen).
Steam Methane Reforming with
Carbon Capture and Sequestration.
Currently, the most common method
for producing hydrogen uses natural
gas (methane) as a primary feedstock
for SMR. Until recently, few have paid
38
H
attention to CO2
emissions from SMR;
however, with the increasing importance
placed on decarbonization in the power
generation sector, SMR is generally only
viewed as a legitimate decarbonization
technique when employed with CCS.
Efficient SMR processes can produce
hydrogen (H2) from methane (CH4
water (H2O) while emitting CO2
) and
at a rate
of about 90 pounds per million Btu (lb/
MMBtu) of fuel produced. However, additional
CO2
emissions can be attributed
to the SMR process.
Significant energy input is required
for the SMR process (heat and steam).
When including CO2
generation, the effective CO2
emitted from their
emission
rate for electric production is about 160
lb/MMBtu. In comparison, the CO2
emission
factor from direct combustion of
natural gas in power generating equipment
is far less, approximately 117 lb/
MMBtu of fuel consumed.
Based on these approximations, the
effective CO2
emissions from the entire
SMR process would need to be reduced
by about 30% for this hydrogen
production method (and, ultimately, hydrogen-fired
power generation) to begin
decarbonizing. Adding CCS can help, but
adds other complications, including the
increased energy requirement to operate
a CCS installation and the multiple
exhaust streams (SMR process and energy
generation) requiring treatment. Ultimately,
with the current limitations of
CCS technology, blue hydrogen has only
a slightly smaller carbon footprint than
grey hydrogen, with significantly higher
capital and operating costs.
Electrolysis of Water. Hydrogen produced
by the electrolysis of water, using
electricity from renewable energy sources,
has low CO2
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emissions directly attributed
to the process. Advantages of tying
renewable energy sources to this hydrogen
production process are twofold:
■ A near-zero CO2
-emitting source of energy
is used in the production of hydrogen.
■ The storage of hydrogen for later use in
power production helps balance longterm,
excess renewable power produced
during lower demand periods
and insufficient renewable power produced
during higher demand periods.
This storage of excess renewable energy
has been a challenge in the industry
and is only partially addressed by using
batteries for shorter periods of storage
and smaller discharge capacities. Figure
1 highlights some of the more wellknown
energy storage technologies,
showing hydrogen's potential to fill a
large gap at the high end of both axes.
Hydrogen's potential for high-capacity,
extended-duration energy storage is perhaps
its biggest selling point as we move
toward decarbonization with renewables
as the predominantly growing asset
class. But what are the environmental
impacts of the process? Let's look at air
quality and water resources.
Because there are no significant air
emission sources at an electrolysis plant,
air permitting issues are not expected to
be significant. However, there are disperPOWER
| October 2021
1. This graph shows the storage capacity
(horizontal axis) and discharge duration (vertical
axis) of four common energy storage technologies.
Courtesy: POWER Engineers
http://www.powermag.com
POWER October 2021

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