(614c) Ammonia As Hydrogen Carrier to Unlock the Full Potential of Green Renewables

Ammonia as hydrogen carrier to unlock the full
potential of green renewables

Camel Makhloufi; Olivier Pierre, Nouaamane
Kezibri, Alexi Liedes
(ENGIE Lab CRIGEN; St Denis; France)

For decades, grid-scale energy storage has been
used to balance load and demand within an energy generation system composed
mainly of base load power sources enabling thus to large nuclear or thermal
generating plant to operate at peak efficiencies. Energy storage has
contributed over the time to meet peak demand and regulate frequency beside
peak fossil fuel power plant who usually provided the bulk of the required
energy.  In the aforementioned context
where inherent variability of the power generation asset was mainly a minor
issue, energy storage capacity remains nevertheless limited for economic reason
storing electricity during low electricity demand and releasing it back into
the grid during high demand, typically over a daily cycle. In a context of a
global spectacular decrease in levelized cost of renewable electricity
(typically PV or onshore/offshore wind) observed in the recent years, the
European Commission  as a clear front
runner in the fight against climate change has set as soon as the year of 2014
a committing objective of 27% for the share of renewable energy consumed in the
European Union by 2030. This objective which was later confirmed in its
intention in 2015 when the European commission ratified the Paris Agreement is now
regarded as a conservative objective for the EU, the penetration of RE being
lately advised to be further accelerated to 34% by 2030 [1].

Energy storage is acknowledged has a decisive
element to insure a reliable and efficient penetration of renewable electricity
in the energy system and starting from its role as initially thought, it is now
expected from a portfolio of energy storage means to offer a multitude of
services . Depending of the situation, energy storage technologies must have
the capability to provide key services like grid services adequacy (congestion
management, curtailment reduction) or ancillary services (frequency response,
black start, voltage) but also the ability to react within seconds to large
electrical load changes. Finally, it is projected for energy storage to shortly
contribute to the decarbonization of other energy intensive sectors thanks to
the sectorial integration of the power sector with transport, the industry and
the heating and cooling sectors. If battery systems reveals to be decisive
components of the energy management system especially for fast response
services, hydrogen based energy carriers appear as one of the only solution
when it comes to seasonal energy storage of large energy quantity and more
specifically for all situation dealing with a large energy-to-power ratio
situation. Also, in this new energy paradigm where distributed renewable generation
cohabit with increasingly larger wind or PV power plant located farther away
from consumption site, the ability to store energy under the form of a
dispatchable energy carrier is a key element

As a versatile and flexible energy storage
mean, green hydrogen produced by electrolysis through power-to gas offer
compelling reasons for its breakthrough penetration into the energy system.
Hydrogen has the unique capability to significantly and potentially
simultaneously decarbonize several energy consuming sectors through
electrification. Hydrogen can be seen as a renewable electricity vector with
ability to be transported from green electricity surplus area to energy
consuming one with minimum losses. This allow for instance to consider
renewable electricity transport from neighboring or distant countries but also
to improve profitability of offshore energy harvesting.

There is so far a great deal of
discussion and research about the most efficient way to transport hydrogen
according to distance and volume. So far, only a few studies focused on hydrogen
transportation cost and most of them demonstrated that hydrogen transportation
cost shall not be neglected. As many hydrogen transportation technologies are
available, there is a critical need for techno economic evaluation in order to
obtain reliable hydrogen transportation costs and address the technological
challenges involved.

Amongst all means, ammonia appears
to be one the most promising hydrogen carriers. Ammonia is easily liquefied by
compression at 1 MPa and 25°C and shows a vapor pressure similar to propane.
Ammonia presents a high hydrogen gravimetric density of 17.8 % by weight and simultaneously an impressive volumetric hydrogen
density with approximately 108 kg H₂/m3 embedded in liquid
ammonia at 20 °C and 8.6 bars. Comparing this to advanced hydrogen storage systems,
e.g. metal hydrides, which store H₂ up to 25 kg/m³ or to liquefied
hydrogen (1,5 time lower) the advantage of ammonia in carrying hydrogen per
unit volume is significant[1]. This
generally translate for instance in ammonia providing a lower cost per unit of
stored energy compared to hydrogen as calculated for instance in previous study
(storage over 182 days ammonia storage would cost 0.54 $/kg-H2 compared to 15
$/kg-H2 of pure hydrogen storage).

In addition to that, thanks to
the large return of experience regarding ammonia chemistry, manufacturing or
handling but also using ammonia existing infrastructure for storage and
transport, ammonia can be used as a profitable energy carrier for hydrogen
distributed generation using compact ammonia decomposition reactors. This
possibility is generally promoted by the fact that ammonia decomposition has a
single feed stream and is therefore accomplished in a single step which leads
to significant cost advantage in consequence of reduced balance-of-plant (BOP).
This contrast particularly with the multi-step process inherent for instance in
steam reforming of hydrocarbons or in methanol reformaing. This provides key
opportunities for decentralized power generation thanks to hydrogen fuel cells
but also pave the way toward on-board ammonia decomposition for fuel cell
vehicule application. Besides this, ammonia also have the capability to be used directly for centralized
power generation in ammonia turbine, in distributed power generation through
the use of high temperature solid oxide fuel cells or mobility application in
direct combustion engine. For all considered
possibilities, ammonia has the unique features to behave as a CO2-free energy
storage mean unlike other hydrogen carriers like methanol, methanol, formic
acid and all Fischer-Tropsch product which release carbon oxides during their
use.

In this presentation, the potential of ammonia
as hydrogen carrier for large scale hydrogen transportation will be discussed on
the basis of both modelling and experimental work.

Thanks to the in-house HYTAC calculation tool (Hydrogen
Transportation Analysis and Costing) developed within ENGIE Lab CRIGEN to compute
the hydrogen transportation cost, several large scale hydrogen production and transportation
scenario are analyzed for various renewable electricity sourcing and according to
different demand scenario and transportation distance. The potential of ammonia,
liquid organic hydrogen carrier, methanol and SNG as hydrogen carrier for the
long distance transportation of green hydrogen from several areas of important renewable
energy technical potential to oversea utilization point is analyzed and
compared. In the presented work, the entire process value chain is considered from
renewable electricity sourcing, green hydrogen production, hydrogenation process,
maritime transportation, dehydrogenation and final utilization of hydrogen for
mobility or industrial applications. A cost breakdown analysis is provided
helping to define the main contributor to the levelized cost of delivered
energy and demonstrate R&D efforts to be done to reach a economic profitability.

Also, as far as ammonia is concerned, the
question of green hydrogen recovery using a centralized or a decentralized
ammonia cracker is still unanswered. First, centralized fired heated ammonia
cracker does not exist so far at size to produce hundred of tons of hydrogen
per day. Then, considering the stringent limit in ammonia content into the
hydrogen feeding a PEM fuel cell (0.1 ppm), selective dehydrogenation reactor
are required in order to reduce purification cost of the forming gas produced.
In this presentation, first results of experiments performed on an innovative compact
decomposition reactor will be introduced. Obtained performances will be compared
on the technical and economic point of view with a designed centralized
cracker.