Page 38 - Energize April 2021

TECHNICAL

advantage during times when the turbine must operate as spinning
reserve when renewable generation is at a high level. In this scenario, the
gas turbine can be operated at very low loads and when required, is able
to deliver power very quickly because it does not need to be switched on
first. In contrast to this, single combustor gas turbines cannot be turned
down to similarly low levels and eventually would have to be turned off,
with the disadvantage of requiring longer time to get to operational state,
with penalties in engine lifetime due to start-stop cycles. 3

Ammonia as an alternative turbine fuel
Storage and transportation are essential to the successful use of
“green hydrogen”. While H 2 has the advantage of high gravimetric
a energy density, the difficulties with storage, such as large storage
volumes, the extreme low temperatures and high pressures required
for liquefaction, and limited existing infrastructure are considered
stumbling blocks in the use of H 2 as fuel for gas turbines. One solution
is to use a H 2 carrier, such as ammonia, for the transportation and
storage of the fuel, and crack it back to H 2 at the user. The properties
of ammonia make storage much easier and infrastructure to transport
ammonia already exists.
Ammonia, which is a compound consisting of H 2 and nitrogen, is a
highly efficient hydrogen carrier, and it can also be directly combusted
as fuel. Expectations are that early introduction of ammonia-based
power-generation equipment will promote ammonia’s future use as
b a carbon-free fuel. Japan for instance has produced a road map for
adoption of ammonia as a fuel. 1
Several manufacturers are developing ammonia fuelled turbines,
and the topic is being researched at several institutes. Because
ammonia has a low combustion speed, it requires a much larger
combustor. And because ammonia contains nitrogen, any system
using it as a fuel will need to tackle the “fuel NOx” generated.
Current development of 100% ammonia fuelled turbines is limited
to smaller sized turbines, although Mitsubishi Power has commenced
6
development of a 40 MW class gas turbine fuelled 100% by ammonia.
In addition, the company has developed a system which reconverts
ammonia into hydrogen and nitrogen using the exhaust heat of the gas
turbine and applies it to the hydrogen gas turbine (Figure 7).
NOx generated by the oxidation of nitrogen in the fuel by
combustion is a challenge in the direct combustion of ammonia, and
development in this area is aimed mainly at NOx reduction. 5 n
c
References
Figure 6: Sequential combustor designs (a) Ansaldo GT26, (b) Ansaldo 1. G Ceccherini, et al: “Retrofitability of DLN/DLE systems”
GT36, (c) Kawasaki 2. GE: “Can GE’s gas turbines run on hydrogen fuel?”
3. J Goldmeer: “Power to gas: hydrogen for power generation”, General
Electric Company, 2019.
4. A Ciani, et al: “Superior fuel and operational flexibility of sequential
combustion in Ansaldo Energia gas turbines”, JGPPS, October 2019.
5. ETN: “Hydrogen gas turbines: the path towards carbon zero gas turbines”,
European Turbine Network, 2020.
6. M Page-Bailey: “Mitsubishi Power developing breakthrough ammonia fired
turbine system”, Chemengonline.com, 2 March 2021.

Figure 7: Ammonia cracking using exhaust heat (Mitsubishi) Send your comments to rogerl@nowmedia.co.za

3
3
Density at NTP (kg/m ) Boiling point °C Liquefaction pressure (bar) Liquid density (Kg/m )
Hydrogen 0,08375 -253 N/A 70,8
Ammonia 0,769 -33 10 bar 600
Table 2: Comparison of hydrogen and ammonia characteristics

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