H2Tech - Q4 2021 - 34

INFRASTRUCTURE AND DISTRIBUTION
H2 blending in natural gas pipelines-
technological challenges and opportunities
G. VALLIOS, METRON Energy Applications, Athens, Greece
H2 is expected to play an important
role in the energy transition, reinforcing
the use of renewable energy resources
and providing a low- to no-carbon footprint.
H2
in the universe, including the nuclear fusion
reactions of our own sun; however,
its utilization as an energy agent is limited,
due to the challenges of producing and
transporting it for use as an energy carrier.
This article reviews the potential for transporting
H2
through natural gas pipelines,
including the associated technical challenges
and opportunities.
Blending concept, benefits and challenges.
The mixing of H2
with natural
gas can significantly reduce greenhouse
gas emissions since the combustion of
H2
is
produces no greenhouse gases-this
is under the assumption that the H2
produced from renewable energy resources
(wind, solar, biomass) or fossil
resources with carbon capture and storage
(CCS). The social and environmental
benefits associated with the hydrogen
blend component to natural gas are obvious:
it reduces carbon oxides (COx
fur oxides (SOx
), nitrogen oxides (NOx
), sul)
and
particulate matter emissions.
An economic incentive exists for the
use of renewable energy surplus, enhancing
the sustainability of natural gas supply
systems, since natural gas can be utilized
also after the fossil transient era. More300
psig: H2
is an abundant source of energy
over, an extended operational life of conventional
power plants that are presently
fueled by natural gas can be achieved.
blending mixture properties.
H2 has a high heating value of ΔΗΗ2
H2
=
120,000 kJ/kg, and a low density of ρΗ2
= 0.089 kg/m3
gas, where indicative values are ΔΗNG
48,000 kJ/kg and ρNG
= 0.76 kg/m3
at
ambient conditions. The heating value of
the mixture depends on the composition
of the natural gas, H2
centage of H2
purity and the perin
the mixture, and can be
obtained using Eq. 1:
Hmixture
where:
Hmixture
= ΔΗmix + ∑xi
after mixing
ΔΗmix= Enthalpy of mixing
Xi
= Mole fraction of component i
in the system
blending of H2
Hi = Enthalpy of pure component i
Therefore, a 10% per mole fraction
in a natural gas pipeline results
in an increase of enthalpy of 2% for
the gas mixture.
Although blending ratios are usually
expressed in volumetric percentages, the
H2
share to the increase of gas mixture
) emis).
heating
value and, subsequently, to the
potential carbon dioxide (CO2
sions savings, is low due to the low volumetric
energy density-roughly 1/3 of 1
of methane (CH4
For energy offtakers, it is important that
300 psig:
H2
, CO2
, CH4
A
B
C
FIG. 1. Pressure swing adsorption (PSA)
schematic.
34 Q4 2021 | H2-Tech.com
5 psig:
H2
, CO2
, CH4, CO
the combustion conditions and Wobbe
index are ensured within the range of the
end-users' operational conditions (i.e., a
gas turbine or power plant). Because the
mixture can be enriched to higher percentages
of H2
, it is possible to extract the H2
downstream of the gas pipeline section.
× Hi
(1)
= Total enthalpy of the system
, compared to natural
=
Methods of downstream extraction.
In the case of high H2
are discussed here.
Pressure swing adsorption (PSA).
PSA, shown in FIG. 1, operates utilizing adsorption
media that have a correlation of
surface adsorption vs. gas partial pressure.
As the gas pressure increases, the concentration
of adsorbed species on the surface
increases. The substances adsorbed in
case of the gas mixture are CH4
CO, whereas the H2
, CO2 and
passes through the
adsorption bed.
Since the adsorption bed is saturated
for a designated time for a designated flow
and pressure condition or duty, a standby
configuration of beds is used so that the
saturated bed is regenerated during the
filtering process.
The method is suitable for H2
separation
at flowrates of 50 Nm3/hr-200,000
Nm3/hr at an elevated pressure of 150
psig-300 psig. While a good H2
purity
level is ensured, a small percentage is expected
to be adsorbed on the surface of
the medium and then removed during the
bed regeneration.1
Membrane separation technology.
This technology works efficiently with
high concentrations of H2
, ensuring good
efficiency with certain membrane technologies
that can reach 100% purity with
adequate membrane selection. Due to the
high differential pressure required across
the membrane for H2
should be compressed to high pressures;
therefore, this technology is suitable for
high-pressure pipelines.
Electrochemical H2
separation.
Known as H2 pumping, this technology
is based on the gas mixture compression.
However, it is not as mature as PSA or
membrane separation.
percentages in the
downstream
gas blending, applicable extraction technologies
separating the H2
recovery, the flow
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