H2Tech - Q4 2021 - 24

POWER AND UTILITIES
Power to gas, liquids, chemicals: An approach
to industrial decarbonization with H2
S. SAKTHIVEL, Tata Consulting Engineers Ltd., Mumbai, India
Around the world, electricity is being
generated from renewable resources like
sun, wind, hydro, tidal and geothermal.
These renewable energy technologies
have been advanced in recent decades,
and prices for renewable energy are dropping,
allowing renewable energy to be
used as a substitute for some fossil fuel
applications. However, some energy systems
still require clean fuels or chemicals
instead of electricity. The electricity produced
from renewables can be converted
into gas, synthetic fuels, chemicals and
industrial/residential heating, which are
referred to as " power-to-X " or " power-togas "
technologies.
FIG. 1
depicts
renewable
electrical
and
power to produce a gaseous fuel (H2
methane), a liquid fuel (methanol, diH2
Electrolysis
CO2
H2
Methanation
Dehydration
H2
H2
Power
to gas
CH4
Feedstocks for
many industries
like NH3
Power to chemicals
CH3
OH
DME
Power to liquids
FIG. 1. A look at power to gas/liquid/chemical feedstock.
Solar PV
FIG. 2. Methane from green H2
24 Q4 2021 | H2-Tech.com
and CO2
.
Electrolysis
CO2
H2
Synthetic
fuel
Industrial/
residential
heating
Power to heat
O
CO2
H2
to CO
(Inverse CO shift)
Electrochemical reduction
Co-electrolysis
Syn Gas
(CO + H2
)
Fischer Tropsch
Heat generation
methyl ether and synthetic gasoline, diesel
or kerosene), an industrial feedstock (e.g.,
ammonia) and industrial/residential heat
by using various technologies. This article
describes available technologies for the
production of clean fuels and chemical
and industrial feedstocks from renewable
sources, along with their levels of maturity
and market opportunities and challenges.
Power to gas. The intention of powerto-gas
technology is to replace fossil fuels
usage in the industrial sector, which could
be a key element to long-term decarbonization.
Almost all energy sectors are undergoing
substantial changes in light of
the energy transition to promote better
efficiency, reduce emissions and increase
the use of renewable energy. The use of
Electricity
H2O + CO2
H2O + CO2
power-to-gas technology can help achieve
these goals. The high energy content of
two gases like H2
and synthetic methane
are produced from the power-to-gas process
by the water electrolysis and methanation
processes, respectively.
Hydrogen. Water electrolysis technology
splits the water into hydrogen (H2
and oxygen (O2
)
) gas molecules by using
a direct-current (DC) power supply from
preferably renewable sources. A simple
water electrolysis unit consists of an anode
and a cathode immersed in the electrolyte
solution [commonly potassium
hydroxide (KOH) and sodium hydroxide
(NaOH)]. The electrodes are connected
through an external DC power supply. At
the cathode, the electrons combine with
the H2
protons to produce H2
and O2
. Then, H2
ions move toward the cathode, whereas
hydroxide ions move toward the anode.
H2
and anode, respectively.
Water electrolysis is categorized into
four types based on their electrolyte and
ionic agents (OH-
, H+, O2
-):
1. Alkaline water electrolysis
(AWE)
2. Proton exchange membrane
electrolysis (PEM)
3. Solid oxide electrolysis (SOE)
4. Anion exchange membrane
electrolysis (AEM).
At present, AWE and PEM electrolysis
are the prominent technologies being
commercialized worldwide. Typically,
CH4
+ H2
O
gases develop at the cathode
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