POWER October 2021 - 40

HYDROGEN
2. This graph depicts the relationship between
the percent hydrogen in fuel blend
(horizontal axis) and the CO2 emission factor
(left-hand vertical axis) and corresponding reduction
in CO2 emissions compared to natural
gas firing (right-hand vertical axis). Courtesy:
POWER Engineers
sion-related requirements, particularly
those associated with venting hydrogen
into the atmosphere during startup,
shutdown, or malfunction events.
These vents are typically designed as
an elevated flare (unlit) with the requisite
radiative heat modeling that ensures a
safe zone around the vent. In addition,
appropriate light-gas dispersion modeling
studies ensure that the released hydrogen
plume is safely dispersed.
Hydrogen Combustion for Power
Generation
As fossil-fueled power generating plants
are retired in lieu of renewable energy production,
having the ability to deliver highcapacity,
extended-duration decarbonized
power becomes increasingly important. The
shift of baseload generation to renewables
makes hydrogen an increasingly attractive
option for times when power demand is
high and renewables are not available.
To generate utility-scale power during
peak demand, hydrogen-fired combustion
turbines are the technology of choice.
Currently, hydrogen must be blended
with natural gas. Most combustion turbine
manufacturers claim that existing
fleets can burn a fuel blend with up to
25% hydrogen by volume without burner
modification. As technology quickly advances,
the introduction of turbines that
burn 100% hydrogen is coming soon.
Permitting Considerations and
Design Implications
There are, however, environmental issues
associated with hydrogen combustion
for power generation. A common
assumption is that hydrogen is a cleanburning
fuel, free from emissions of
harmful air pollutants. While hydrogen as
a fuel does not emit greenhouse gases,
a combustion unit uses ambient air to
supply the oxygen in the fuel combustion
process. This air contains nitrogen
that, in the presence of heat and oxygen,
forms oxides of nitrogen (NOx
). NOx
emissions are highly regulated air pollutants
by federal, state, and local environmental
agencies.
NOx
emissions increase when comparing
hydrogen combustion to natural
gas combustion. Hydrogen is lighter,
burns hotter, and carries one-third the
heating value on a volumetric basis compared
to natural gas. Because it burns
hotter, NOx
crease in NOx
emissions are higher. This inemissions
will likely trigger
additional air permitting complications
for existing units, and challenges in the
design and operation of new units.
For existing units, adding the capability
to burn 25% hydrogen to an air permit
could be considered a change in the
method of operation, triggering additional,
more-extensive air permitting requirements.
If there is no increase in NOx
sions, the air permitting complications
emisEnsuring
Plant Reliability
and Resiliency During Critical
Operations Processes
* Reduce unplanned outages and mitigate risks
* Ensure effective responses to abnormal
conditions
* Boost plant performance throughout the asset
lifecycle
* Achieve higher production goals by connecting
workers and processes
PREVENT. PROTECT. PERFORM.
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POWER October 2021

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