H2Tech - Q4 2021 - 28

POWER AND UTILITIES
Power to liquid. The power-to-liquid
process can be used to produce liquid
hydrocarbons from water and CO2
using electricity. The power-to-liquid
process contains three steps:
1. H2
generation from a water
electrolyzer, using renewable
electricity
2. Capture and purification of
CO2
process or offgases, where rich
CO2
from post-combustion
is available
3. Conversion and upgrading
to produce gasoline, kerosene
and diesel.
Two principal pathways are available
to produce liquid hydrocarbons from
renewable energy via (a) the FischerTropsch
(F-T) process and (b) methanol
synthesis from the hydrogenation
of CO2
of CO2
provide a high technology readiness
Generally, stationary sources of CO2
by
are available in the cement industry,
iron and steel plants, power plants and
oil refineries, where fossil fuels are used
as feedstock. Typically, 1 metric ton of
methanol can be produced from 1.38
metric tons of CO2
, as per the stoichioproduced
.
metric
calculation. The viability of this
process will increase with H2
from renewable routes and greater availability
of low-cost CO2
Dimethyl ether (DME). DME is
produced via the dehydration of methanol.
DME can be used as an alternative
fuel in diesel motors, and it emits low
emissions of particulate matter (PM)
and NOX
; therefore, it can be considered
a sustainable fuel.
Synthetic fuels. Generally, F-T synthesis
requires CO and H2
and electrochemical reduction
. Furthermore, dimethyl ether
(DME) is produced from the dehydration
of methanol. Both the F-T process
and methanol from the hydrogenation of
CO2
level (TRL) of between 8 and 9. The following
section describes the significance
of value-added liquid fuels like methanol
and synthetic hydrocarbon fuels.
Methanol. Methanol can be produced
through two new routes: (a)
electrochemical reduction and (b) hydrogenation
of CO2
. The CO2
can be
converted into value-added chemicals
like formic acid, methane, ethylene and
ethanol by using electrochemical reduction
or electrocatalytic process. This process
can be considered a viable strategy
for mitigating greenhouse gas emissions
and can potentially reduce dependence
on fossil fuels. It has gained significant
attention in connection with renewable
energy and due to its viable controllability,
modularity and simple scale-up. The
process also operates at room temperature
and ambient pressure. However, this
process has not yet been commercialized
because the yields do not meet industrial
needs. In 2021, a research agreement was
signed by Shell and the National University
of Singapore to produce cleaner
fuels (ethanol) and useful chemicals (npropanol)
from CO2
.
An alternative route for methanol
.3 FIG. 4 shows the process flow
as feedstock.
production is the hydrogenation of H2
and CO2
diagram for methanol production using
renewable power and CO2
28 Q4 2021 | H2-Tech.com
hydrocarbon fuels. The captured CO2
to produce
is
converted to CO through an inverse CO
shift reactor, using the reverse water-gas
shift (RWGS) reaction. FIG. 5 depicts
the process flow diagram for producing
synthetic gasoline, diesel and kerosene,
using upgraded hydrocracking, isomerization
and distillation processes.
Power to heat. Renewable power can
also be used to enhance heat and steam.
Heat pumps and passive thermal storage
are available for the utilization of renewable
energy as heat energy. This uses
large-scale heat pumps or electric boilers
for industrial processes such as heating,
drying, distillation, etc. Power to heat
has great potential to reduce energy consumption
and greenhouse gas emissions
and to replace fossil fuel usage.
Opportunities
and
challenges. A
number of specific opportunities are
available for the utilization of power-togas
technology:4
* Existing energy systems and
their infrastructure can be used
for the integration of renewable
energy sources
* Regional economies can be
strengthened
* Emissions may be reduced in
various energy sectors
* A significant share of renewable
energy would be increased with
greater flexibility of the system.
Several challenges to power-to-gas technology
also exist:
* A policy framework must be
established for power-to-gas
technology as the system
balancing technology
* CAPEX and OPEX of the
technologies (including CO2
capture, water electrolysis, dry
reforming, electrochemical
reduction, and storage and
transportation of low-density
fuels like H2
) are expensive
and must be reduced through
research and development
* A smart management system
with an information technology
(IT) network is needed
for high effectiveness for
power-to-gas technology.
Takeaway. Power-to-gas technology is a
long-term strategy to decrease emissions
from fossil fuels and help achieve the
industrial ambitions of the energy transition.
It derives a great advantage from
renewable energy due to the decreasing
cost of renewable energy and its low
carbon footprint. Technologies are being
commercialized around the world in
the emerging areas of power to gas (e.g.,
H2
and methane), power to liquid (e.g.,
methanol, DME, synthetic H2 fuels) and
power to chemicals (e.g., ammonia).
LITERATURE CITED
1
Sakthivel, S., " Way forward to carbon-free
electricity for e-mobility, " Chemical Industry Digest,
June 2019.
2 Sakthivel, S., S. S. Swami and A. Choudhari,
" Green hydrogen: A perspective, " Proceedings
of the 35th Indian Engineering Congress on
Engineering for Self-Reliance and Sustainable
Goals, December 18-20, 2020, India.
3
Sakthivel, S., " Pathways and industrial approaches
for utilization of carbon dioxide, " TCE Tech
Speak, March 14, 2018, online: https://www.tce.
co.in/blogs/pathways-industrial-approaches-forutilization-of-co2
4
Lewandowska-Bernata, A. and U. Desideri,
" Opportunities of power-to-gas technology, " 8th
International Conference on Applied Energy,
Energy Procedia 105, 2017.
S. SAKTHIVEL is a Senior
Technologist at the Technology
Group of Tata Consulting Engineers
Ltd. in Mumbai, India. His areas of
focus include green chemicals, green
fuels, the energy transition and
decarbonization, with responsibility
for the evaluation of emerging technologies and
commercialization. Dr. Sakthivel has experience in
process engineering; technology analysis, screening
and selection; techno-economic analysis; pilot setups;
process hazard analysis; basic, applied and market
research; and powder and science technology.
He holds a PhD and has published several articles
in national and peer-reviewed international journals.
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