H2Tech - Q1 2022 - 24

SPECIAL FOCUS ADVANCES IN HYDROGEN TECHNOLOGY
gas at room temperature, as with H2
it is
common to hear it referred to by color. As
illustrated by FIG. 1 and expounded upon
below, these colors correspond to different
methods of producing ammonia.
Brown ammonia is produced via
the Haber-Bosch process from gray or
brown H2
as feedstock. Gray H2
, both of which use fossil fuels
is extracted from
natural gas by means of steam reforming,
while brown H2
gasification. Both colors of H2
is created via coal
emit CO2
during production and release it into the
atmosphere, as does the Haber-Bosch
process itself. Brown ammonia accounts
for most of the ammonia produced since
the Haber-Bosch process was developed.
Blue ammonia is produced through
the same methods as brown ammonia,
but carbon capture and storage is integrated
with the traditional process to
avoid CO2
escaping to the atmosphere.
renewable, CO2
Green ammonia is produced using
-free energy sources, and
correspondingly without the use of hydrocarbons.
The H2
it uses as its prime
raw material is produced via water electrolysis
using 100% sustainable electricity
sources. Green ammonia production
also requires air separation units (ASUs)
to produce N2
. FIG. 2 depicts the production
and applications of green ammonia.
Green ammonia in depth. A standard
green ammonia production unit comprises
three modules:
1. H2
This generates H2
generation and supply unit:
via water
electrolysis, and is suitable
for the storage and handling
of H2
Electrolyzer
Green H2
O2
as byproduct
N2
ASU
Sustainable energy
generation
Process
FIG. 2. Green ammonia production routes and their applications.
24 Q1 2022 | H2-Tech.com
Use
Green NH3
production
Expanded Uses
a. Energy store for
electricity generation
b. Transport fuel
c. Heat transfer agent
Existing Applications
a. Fertilizers
b. Refrigeration
c. Explosives
d. Textiles and
pharmaceuticals
and its co-product of O2
,
Challenges and mitigation. The production,
storage, distribution and transportation
of green H2
all represent key
challenges to green ammonia production.
The transportation of low-density
fuel such as H2
is very difficult and may
thus adding additional
require new or modified infrastructure
developments,
costs to H2 production. Transportation
leakage.
tralized H2
To mitigate these challenges, de-cenproduction
could be introduced
into the fertilizer, methanol, iron
and refining industries, all of which require
large quantities of H2
. These industries
would install electrolyzers within
their boundary limits that utilize electricity
generated by solar and/or wind
problems also include delivery costs, H2
purity and minimizing H2
which is released into
the atmosphere
2. N2 generation and supply unit:
This generates N2
via an ASU
and is suitable for the storage
and handling of N2
3. Ammonia production and storage:
This synthesizes ammonia, as well
as handling its storage.
A typical large-scale green ammonia
production plant consumes
10 MWh-14 MWh of energy per metric t
of green ammonia produced. While this
represents greater proportional energy
consumption than seen in brown H2
,
the cost is offset by the environmental
benefits (i.e., lower emissions). Despite
evidence of growing interesta
, further research
and development are still required
to lower the cost and improve the efficiency
of green H2
-related technologies.
plants via a power grid. This renewable
electricity is transportable through existing
power transmission networks and
would then be used to produce H2
storage would remain necesonsite,
doing away with the need to transport
it. H2
sary, however, as ammonia production
requires round-the-clock availability of
H2
be installed, and the excess H2
than needed should
temporarily
stored onsite for use when renewable
electricity is not available.
Takeaway. Ammonia production is presently
a large contributor to global CO2
emissions due to its dependence on fossil
fuels. The major energy requirements,
along with most of the CO2
occur due to the H2
emissions,
production process
upon which ammonia synthesis relies.
Green ammonia is therefore only feasible
if H2
production is made fully dependent
on renewable energy sources. With that
condition met, ammonia is a carbon-free
alternative to hydrocarbons as an agent
for carrying and storing energy. Existing
technologies, infrastructure and policies
make ammonia convenient and safe to
transport, and technologies for green ammonia
production are undergoing rapid
development due to increased research
into energy efficiency. Areas of further
research in the H2
supply chain include
storage and H2
cost reduction and better performance
for electrolyzers, H2
transportation
infrastructure.
NOTES
a
Examples of green ammonia projects currently
under construction include a 4-GW green ammonia
plant in Saudi Arabia by NEOM, Air Products and
ACWA Power; the H2U Eyre Peninsula Gateway
Hydrogen Project in Australia; an engineering and
procurement contract signed by CF Industries
Holdings, Inc. with thyssenkrupp for the Company's
green ammonia project in its Donaldson, Louisiana
(U.S.) plant; and Yara International ASA's plan to
build a renewable H2
plant in Norway.
DR. S. SAKTHIVEL is a Senior
Technologist at the Technology
Group of Tata Consulting Engineers
Ltd. in Mumbai, India. His primary
focus is on green chemicals, green
fuels, the energy transition and
decarbonization, with the
responsibility for evaluating emerging technologies
and commercialization. He 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 science and technology.
He has published several papers in national and
peer-reviewed international journals.
. Therefore, an electrolyzer capable of
producing more H2
Renewable energy
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